Merge tag 'x86-urgent-2024-04-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull misc x86 fixes from Ingo Molnar:

- Follow up fixes for the BHI mitigations code

- Fix !SPECULATION_MITIGATIONS bug not turning off mitigations as
expected

- Work around an APIC emulation bug when the kernel is built with Clang
and run as a SEV guest

- Follow up x86 topology fixes

* tag 'x86-urgent-2024-04-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
x86/cpu/amd: Move TOPOEXT enablement into the topology parser
x86/cpu/amd: Make the NODEID_MSR union actually work
x86/cpu/amd: Make the CPUID 0x80000008 parser correct
x86/bugs: Replace CONFIG_SPECTRE_BHI_{ON,OFF} with CONFIG_MITIGATION_SPECTRE_BHI
x86/bugs: Remove CONFIG_BHI_MITIGATION_AUTO and spectre_bhi=auto
x86/bugs: Clarify that syscall hardening isn't a BHI mitigation
x86/bugs: Fix BHI handling of RRSBA
x86/bugs: Rename various 'ia32_cap' variables to 'x86_arch_cap_msr'
x86/bugs: Cache the value of MSR_IA32_ARCH_CAPABILITIES
x86/bugs: Fix BHI documentation
x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n
x86/topology: Don't update cpu_possible_map in topo_set_cpuids()
x86/bugs: Fix return type of spectre_bhi_state()
x86/apic: Force native_apic_mem_read() to use the MOV instruction

Documentation/admin-guide/hw-vuln/spectre.rst

···
    - System is protected by retpoline
  * - BHI: BHI_DIS_S
    - System is protected by BHI_DIS_S
- * - BHI: SW loop; KVM SW loop
+ * - BHI: SW loop, KVM SW loop
    - System is protected by software clearing sequence
- * - BHI: Syscall hardening
-   - Syscalls are hardened against BHI
- * - BHI: Syscall hardening; KVM: SW loop
-   - System is protected from userspace attacks by syscall hardening; KVM is protected by software clearing sequence
+ * - BHI: Vulnerable
+   - System is vulnerable to BHI
+ * - BHI: Vulnerable, KVM: SW loop
+   - System is vulnerable; KVM is protected by software clearing sequence
 
 Full mitigation might require a microcode update from the CPU
 vendor. When the necessary microcode is not available, the kernel will
···
 	spectre_bhi=
 
 		[X86] Control mitigation of Branch History Injection
-		(BHI) vulnerability. Syscalls are hardened against BHI
-		regardless of this setting. This setting affects the deployment
+		(BHI) vulnerability.  This setting affects the deployment
 		of the HW BHI control and the SW BHB clearing sequence.
 
 		on
-			unconditionally enable.
+			(default) Enable the HW or SW mitigation as
+			needed.
 		off
-			unconditionally disable.
-		auto
-			enable if hardware mitigation
-			control(BHI_DIS_S) is available, otherwise
-			enable alternate mitigation in KVM.
+			Disable the mitigation.
 
 For spectre_v2_user see Documentation/admin-guide/kernel-parameters.txt
 

Documentation/admin-guide/kernel-parameters.txt

···
 					       retbleed=off [X86]
 					       spec_rstack_overflow=off [X86]
 					       spec_store_bypass_disable=off [X86,PPC]
+					       spectre_bhi=off [X86]
 					       spectre_v2_user=off [X86]
 					       srbds=off [X86,INTEL]
 					       ssbd=force-off [ARM64]
···
 			See Documentation/admin-guide/laptops/sonypi.rst
 
 	spectre_bhi=	[X86] Control mitigation of Branch History Injection
-			(BHI) vulnerability. Syscalls are hardened against BHI
-			reglardless of this setting. This setting affects the
+			(BHI) vulnerability.  This setting affects the
 			deployment of the HW BHI control and the SW BHB
 			clearing sequence.
 
-			on   - unconditionally enable.
-			off  - unconditionally disable.
-			auto - (default) enable hardware mitigation
-			       (BHI_DIS_S) if available, otherwise enable
-			       alternate mitigation in KVM.
+			on   - (default) Enable the HW or SW mitigation
+			       as needed.
+			off  - Disable the mitigation.
 
 	spectre_v2=	[X86,EARLY] Control mitigation of Spectre variant 2
 			(indirect branch speculation) vulnerability.

arch/x86/Kconfig

···
 	  stored in floating point, vector and integer registers.
 	  See also <file:Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst>
 
-choice
-	prompt "Clear branch history"
+config MITIGATION_SPECTRE_BHI
+	bool "Mitigate Spectre-BHB (Branch History Injection)"
 	depends on CPU_SUP_INTEL
-	default SPECTRE_BHI_ON
+	default y
 	help
 	  Enable BHI mitigations. BHI attacks are a form of Spectre V2 attacks
 	  where the branch history buffer is poisoned to speculatively steer
 	  indirect branches.
 	  See <file:Documentation/admin-guide/hw-vuln/spectre.rst>
-
-config SPECTRE_BHI_ON
-	bool "on"
-	help
-	  Equivalent to setting spectre_bhi=on command line parameter.
-config SPECTRE_BHI_OFF
-	bool "off"
-	help
-	  Equivalent to setting spectre_bhi=off command line parameter.
-config SPECTRE_BHI_AUTO
-	bool "auto"
-	depends on BROKEN
-	help
-	  Equivalent to setting spectre_bhi=auto command line parameter.
-
-endchoice
 
 endif
 

arch/x86/include/asm/apic.h

···
 #include <asm/mpspec.h>
 #include <asm/msr.h>
 #include <asm/hardirq.h>
+#include <asm/io.h>
 
 #define ARCH_APICTIMER_STOPS_ON_C3	1
 
···
 
 static inline u32 native_apic_mem_read(u32 reg)
 {
-	return *((volatile u32 *)(APIC_BASE + reg));
+	return readl((void __iomem *)(APIC_BASE + reg));
 }
 
 static inline void native_apic_mem_eoi(void)

arch/x86/kernel/apic/apic.c

···
 
 static bool x2apic_hw_locked(void)
 {
-	u64 ia32_cap;
+	u64 x86_arch_cap_msr;
 	u64 msr;
 
-	ia32_cap = x86_read_arch_cap_msr();
-	if (ia32_cap & ARCH_CAP_XAPIC_DISABLE) {
+	x86_arch_cap_msr = x86_read_arch_cap_msr();
+	if (x86_arch_cap_msr & ARCH_CAP_XAPIC_DISABLE) {
 		rdmsrl(MSR_IA32_XAPIC_DISABLE_STATUS, msr);
 		return (msr & LEGACY_XAPIC_DISABLED);
 	}

arch/x86/kernel/cpu/amd.c

···
 
 static void early_init_amd(struct cpuinfo_x86 *c)
 {
-	u64 value;
 	u32 dummy;
 
 	if (c->x86 >= 0xf)
···
 		msr_set_bit(MSR_AMD64_LS_CFG, 15);
 
 	early_detect_mem_encrypt(c);
-
-	/* Re-enable TopologyExtensions if switched off by BIOS */
-	if (c->x86 == 0x15 &&
-	    (c->x86_model >= 0x10 && c->x86_model <= 0x6f) &&
-	    !cpu_has(c, X86_FEATURE_TOPOEXT)) {
-
-		if (msr_set_bit(0xc0011005, 54) > 0) {
-			rdmsrl(0xc0011005, value);
-			if (value & BIT_64(54)) {
-				set_cpu_cap(c, X86_FEATURE_TOPOEXT);
-				pr_info_once(FW_INFO "CPU: Re-enabling disabled Topology Extensions Support.\n");
-			}
-		}
-	}
 
 	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_IBPB_BRTYPE)) {
 		if (c->x86 == 0x17 && boot_cpu_has(X86_FEATURE_AMD_IBPB))

arch/x86/kernel/cpu/bugs.c

···
 u64 x86_pred_cmd __ro_after_init = PRED_CMD_IBPB;
 EXPORT_SYMBOL_GPL(x86_pred_cmd);
 
+static u64 __ro_after_init x86_arch_cap_msr;
+
 static DEFINE_MUTEX(spec_ctrl_mutex);
 
 void (*x86_return_thunk)(void) __ro_after_init = __x86_return_thunk;
···
 		 */
 		x86_spec_ctrl_base &= ~SPEC_CTRL_MITIGATIONS_MASK;
 	}
+
+	x86_arch_cap_msr = x86_read_arch_cap_msr();
 
 	/* Select the proper CPU mitigations before patching alternatives: */
 	spectre_v1_select_mitigation();
···
 
 static void __init taa_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_TAA)) {
 		taa_mitigation = TAA_MITIGATION_OFF;
 		return;
···
 	 * On MDS_NO=1 CPUs if ARCH_CAP_TSX_CTRL_MSR is not set, microcode
 	 * update is required.
 	 */
-	ia32_cap = x86_read_arch_cap_msr();
-	if ( (ia32_cap & ARCH_CAP_MDS_NO) &&
-	    !(ia32_cap & ARCH_CAP_TSX_CTRL_MSR))
+	if ( (x86_arch_cap_msr & ARCH_CAP_MDS_NO) &&
+	    !(x86_arch_cap_msr & ARCH_CAP_TSX_CTRL_MSR))
 		taa_mitigation = TAA_MITIGATION_UCODE_NEEDED;
 
 	/*
···
 
 static void __init mmio_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
 	     boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
 	     cpu_mitigations_off()) {
···
 
 	if (mmio_mitigation == MMIO_MITIGATION_OFF)
 		return;
-
-	ia32_cap = x86_read_arch_cap_msr();
 
 	/*
 	 * Enable CPU buffer clear mitigation for host and VMM, if also affected
···
 	 * be propagated to uncore buffers, clearing the Fill buffers on idle
 	 * is required irrespective of SMT state.
 	 */
-	if (!(ia32_cap & ARCH_CAP_FBSDP_NO))
+	if (!(x86_arch_cap_msr & ARCH_CAP_FBSDP_NO))
 		static_branch_enable(&mds_idle_clear);
 
 	/*
···
 	 * FB_CLEAR or by the presence of both MD_CLEAR and L1D_FLUSH on MDS
 	 * affected systems.
 	 */
-	if ((ia32_cap & ARCH_CAP_FB_CLEAR) ||
+	if ((x86_arch_cap_msr & ARCH_CAP_FB_CLEAR) ||
 	    (boot_cpu_has(X86_FEATURE_MD_CLEAR) &&
 	     boot_cpu_has(X86_FEATURE_FLUSH_L1D) &&
-	     !(ia32_cap & ARCH_CAP_MDS_NO)))
+	     !(x86_arch_cap_msr & ARCH_CAP_MDS_NO)))
 		mmio_mitigation = MMIO_MITIGATION_VERW;
 	else
 		mmio_mitigation = MMIO_MITIGATION_UCODE_NEEDED;
···
 	if (rfds_mitigation == RFDS_MITIGATION_OFF)
 		return;
 
-	if (x86_read_arch_cap_msr() & ARCH_CAP_RFDS_CLEAR)
+	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
 		setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
 	else
 		rfds_mitigation = RFDS_MITIGATION_UCODE_NEEDED;
···
 
 static void __init srbds_select_mitigation(void)
 {
-	u64 ia32_cap;
-
 	if (!boot_cpu_has_bug(X86_BUG_SRBDS))
 		return;
 
···
 	 * are only exposed to SRBDS when TSX is enabled or when CPU is affected
 	 * by Processor MMIO Stale Data vulnerability.
 	 */
-	ia32_cap = x86_read_arch_cap_msr();
-	if ((ia32_cap & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) &&
+	if ((x86_arch_cap_msr & ARCH_CAP_MDS_NO) && !boot_cpu_has(X86_FEATURE_RTM) &&
 	    !boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA))
 		srbds_mitigation = SRBDS_MITIGATION_TSX_OFF;
 	else if (boot_cpu_has(X86_FEATURE_HYPERVISOR))
···
 	/* Will verify below that mitigation _can_ be disabled */
 
 	/* No microcode */
-	if (!(x86_read_arch_cap_msr() & ARCH_CAP_GDS_CTRL)) {
+	if (!(x86_arch_cap_msr & ARCH_CAP_GDS_CTRL)) {
 		if (gds_mitigation == GDS_MITIGATION_FORCE) {
 			/*
 			 * This only needs to be done on the boot CPU so do it
···
 	return SPECTRE_V2_RETPOLINE;
 }
 
+static bool __ro_after_init rrsba_disabled;
+
 /* Disable in-kernel use of non-RSB RET predictors */
 static void __init spec_ctrl_disable_kernel_rrsba(void)
 {
-	u64 ia32_cap;
+	if (rrsba_disabled)
+		return;
+
+	if (!(x86_arch_cap_msr & ARCH_CAP_RRSBA)) {
+		rrsba_disabled = true;
+		return;
+	}
 
 	if (!boot_cpu_has(X86_FEATURE_RRSBA_CTRL))
 		return;
 
-	ia32_cap = x86_read_arch_cap_msr();
-
-	if (ia32_cap & ARCH_CAP_RRSBA) {
-		x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
-		update_spec_ctrl(x86_spec_ctrl_base);
-	}
+	x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
+	update_spec_ctrl(x86_spec_ctrl_base);
+	rrsba_disabled = true;
 }
 
 static void __init spectre_v2_determine_rsb_fill_type_at_vmexit(enum spectre_v2_mitigation mode)
···
 enum bhi_mitigations {
 	BHI_MITIGATION_OFF,
 	BHI_MITIGATION_ON,
-	BHI_MITIGATION_AUTO,
 };
 
 static enum bhi_mitigations bhi_mitigation __ro_after_init =
-	IS_ENABLED(CONFIG_SPECTRE_BHI_ON)  ? BHI_MITIGATION_ON  :
-	IS_ENABLED(CONFIG_SPECTRE_BHI_OFF) ? BHI_MITIGATION_OFF :
-					     BHI_MITIGATION_AUTO;
+	IS_ENABLED(CONFIG_MITIGATION_SPECTRE_BHI) ? BHI_MITIGATION_ON : BHI_MITIGATION_OFF;
 
 static int __init spectre_bhi_parse_cmdline(char *str)
 {
···
 		bhi_mitigation = BHI_MITIGATION_OFF;
 	else if (!strcmp(str, "on"))
 		bhi_mitigation = BHI_MITIGATION_ON;
-	else if (!strcmp(str, "auto"))
-		bhi_mitigation = BHI_MITIGATION_AUTO;
 	else
 		pr_err("Ignoring unknown spectre_bhi option (%s)", str);
 
···
 		return;
 
 	/* Retpoline mitigates against BHI unless the CPU has RRSBA behavior */
-	if (cpu_feature_enabled(X86_FEATURE_RETPOLINE) &&
-	    !(x86_read_arch_cap_msr() & ARCH_CAP_RRSBA))
-		return;
+	if (cpu_feature_enabled(X86_FEATURE_RETPOLINE)) {
+		spec_ctrl_disable_kernel_rrsba();
+		if (rrsba_disabled)
+			return;
+	}
 
 	if (spec_ctrl_bhi_dis())
 		return;
···
 	/* Mitigate KVM by default */
 	setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT);
 	pr_info("Spectre BHI mitigation: SW BHB clearing on vm exit\n");
-
-	if (bhi_mitigation == BHI_MITIGATION_AUTO)
-		return;
 
 	/* Mitigate syscalls when the mitigation is forced =on */
 	setup_force_cpu_cap(X86_FEATURE_CLEAR_BHB_LOOP);
···
 /* Update the static key controlling the MDS CPU buffer clear in idle */
 static void update_mds_branch_idle(void)
 {
-	u64 ia32_cap = x86_read_arch_cap_msr();
-
 	/*
 	 * Enable the idle clearing if SMT is active on CPUs which are
 	 * affected only by MSBDS and not any other MDS variant.
···
 	if (sched_smt_active()) {
 		static_branch_enable(&mds_idle_clear);
 	} else if (mmio_mitigation == MMIO_MITIGATION_OFF ||
-		   (ia32_cap & ARCH_CAP_FBSDP_NO)) {
+		   (x86_arch_cap_msr & ARCH_CAP_FBSDP_NO)) {
 		static_branch_disable(&mds_idle_clear);
 	}
 }
···
 	}
 }
 
-static const char * const spectre_bhi_state(void)
+static const char *spectre_bhi_state(void)
 {
 	if (!boot_cpu_has_bug(X86_BUG_BHI))
 		return "; BHI: Not affected";
···
 		return "; BHI: BHI_DIS_S";
 	else if  (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP))
 		return "; BHI: SW loop, KVM: SW loop";
-	else if (boot_cpu_has(X86_FEATURE_RETPOLINE) &&
-		 !(x86_read_arch_cap_msr() & ARCH_CAP_RRSBA))
+	else if (boot_cpu_has(X86_FEATURE_RETPOLINE) && rrsba_disabled)
 		return "; BHI: Retpoline";
-	else if  (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
-		return "; BHI: Syscall hardening, KVM: SW loop";
+	else if (boot_cpu_has(X86_FEATURE_CLEAR_BHB_LOOP_ON_VMEXIT))
+		return "; BHI: Vulnerable, KVM: SW loop";
 
-	return "; BHI: Vulnerable (Syscall hardening enabled)";
+	return "; BHI: Vulnerable";
 }
 
 static ssize_t spectre_v2_show_state(char *buf)

arch/x86/kernel/cpu/common.c

···
 
 u64 x86_read_arch_cap_msr(void)
 {
-	u64 ia32_cap = 0;
+	u64 x86_arch_cap_msr = 0;
 
 	if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
-		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
+		rdmsrl(MSR_IA32_ARCH_CAPABILITIES, x86_arch_cap_msr);
 
-	return ia32_cap;
+	return x86_arch_cap_msr;
 }
 
-static bool arch_cap_mmio_immune(u64 ia32_cap)
+static bool arch_cap_mmio_immune(u64 x86_arch_cap_msr)
 {
-	return (ia32_cap & ARCH_CAP_FBSDP_NO &&
-		ia32_cap & ARCH_CAP_PSDP_NO &&
-		ia32_cap & ARCH_CAP_SBDR_SSDP_NO);
+	return (x86_arch_cap_msr & ARCH_CAP_FBSDP_NO &&
+		x86_arch_cap_msr & ARCH_CAP_PSDP_NO &&
+		x86_arch_cap_msr & ARCH_CAP_SBDR_SSDP_NO);
 }
 
-static bool __init vulnerable_to_rfds(u64 ia32_cap)
+static bool __init vulnerable_to_rfds(u64 x86_arch_cap_msr)
 {
 	/* The "immunity" bit trumps everything else: */
-	if (ia32_cap & ARCH_CAP_RFDS_NO)
+	if (x86_arch_cap_msr & ARCH_CAP_RFDS_NO)
 		return false;
 
 	/*
···
 	 * indicate that mitigation is needed because guest is running on a
 	 * vulnerable hardware or may migrate to such hardware:
 	 */
-	if (ia32_cap & ARCH_CAP_RFDS_CLEAR)
+	if (x86_arch_cap_msr & ARCH_CAP_RFDS_CLEAR)
 		return true;
 
 	/* Only consult the blacklist when there is no enumeration: */
···
 
 static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 {
-	u64 ia32_cap = x86_read_arch_cap_msr();
+	u64 x86_arch_cap_msr = x86_read_arch_cap_msr();
 
 	/* Set ITLB_MULTIHIT bug if cpu is not in the whitelist and not mitigated */
 	if (!cpu_matches(cpu_vuln_whitelist, NO_ITLB_MULTIHIT) &&
-	    !(ia32_cap & ARCH_CAP_PSCHANGE_MC_NO))
+	    !(x86_arch_cap_msr & ARCH_CAP_PSCHANGE_MC_NO))
 		setup_force_cpu_bug(X86_BUG_ITLB_MULTIHIT);
 
 	if (cpu_matches(cpu_vuln_whitelist, NO_SPECULATION))
···
 		setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
 
 	if (!cpu_matches(cpu_vuln_whitelist, NO_SSB) &&
-	    !(ia32_cap & ARCH_CAP_SSB_NO) &&
+	    !(x86_arch_cap_msr & ARCH_CAP_SSB_NO) &&
 	   !cpu_has(c, X86_FEATURE_AMD_SSB_NO))
 		setup_force_cpu_bug(X86_BUG_SPEC_STORE_BYPASS);
 
···
 	 * Don't use AutoIBRS when SNP is enabled because it degrades host
 	 * userspace indirect branch performance.
 	 */
-	if ((ia32_cap & ARCH_CAP_IBRS_ALL) ||
+	if ((x86_arch_cap_msr & ARCH_CAP_IBRS_ALL) ||
 	    (cpu_has(c, X86_FEATURE_AUTOIBRS) &&
 	     !cpu_feature_enabled(X86_FEATURE_SEV_SNP))) {
 		setup_force_cpu_cap(X86_FEATURE_IBRS_ENHANCED);
 		if (!cpu_matches(cpu_vuln_whitelist, NO_EIBRS_PBRSB) &&
-		    !(ia32_cap & ARCH_CAP_PBRSB_NO))
+		    !(x86_arch_cap_msr & ARCH_CAP_PBRSB_NO))
 			setup_force_cpu_bug(X86_BUG_EIBRS_PBRSB);
 	}
 
 	if (!cpu_matches(cpu_vuln_whitelist, NO_MDS) &&
-	    !(ia32_cap & ARCH_CAP_MDS_NO)) {
+	    !(x86_arch_cap_msr & ARCH_CAP_MDS_NO)) {
 		setup_force_cpu_bug(X86_BUG_MDS);
 		if (cpu_matches(cpu_vuln_whitelist, MSBDS_ONLY))
 			setup_force_cpu_bug(X86_BUG_MSBDS_ONLY);
···
 	 * TSX_CTRL check alone is not sufficient for cases when the microcode
 	 * update is not present or running as guest that don't get TSX_CTRL.
 	 */
-	if (!(ia32_cap & ARCH_CAP_TAA_NO) &&
+	if (!(x86_arch_cap_msr & ARCH_CAP_TAA_NO) &&
 	    (cpu_has(c, X86_FEATURE_RTM) ||
-	     (ia32_cap & ARCH_CAP_TSX_CTRL_MSR)))
+	     (x86_arch_cap_msr & ARCH_CAP_TSX_CTRL_MSR)))
 		setup_force_cpu_bug(X86_BUG_TAA);
 
 	/*
···
 	 * Set X86_BUG_MMIO_UNKNOWN for CPUs that are neither in the blacklist,
 	 * nor in the whitelist and also don't enumerate MSR ARCH_CAP MMIO bits.
 	 */
-	if (!arch_cap_mmio_immune(ia32_cap)) {
+	if (!arch_cap_mmio_immune(x86_arch_cap_msr)) {
 		if (cpu_matches(cpu_vuln_blacklist, MMIO))
 			setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
 		else if (!cpu_matches(cpu_vuln_whitelist, NO_MMIO))
···
 	}
 
 	if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
-		if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA))
+		if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (x86_arch_cap_msr & ARCH_CAP_RSBA))
 			setup_force_cpu_bug(X86_BUG_RETBLEED);
 	}
 
···
 	 * disabling AVX2. The only way to do this in HW is to clear XCR0[2],
 	 * which means that AVX will be disabled.
 	 */
-	if (cpu_matches(cpu_vuln_blacklist, GDS) && !(ia32_cap & ARCH_CAP_GDS_NO) &&
+	if (cpu_matches(cpu_vuln_blacklist, GDS) && !(x86_arch_cap_msr & ARCH_CAP_GDS_NO) &&
 	    boot_cpu_has(X86_FEATURE_AVX))
 		setup_force_cpu_bug(X86_BUG_GDS);
 
-	if (vulnerable_to_rfds(ia32_cap))
+	if (vulnerable_to_rfds(x86_arch_cap_msr))
 		setup_force_cpu_bug(X86_BUG_RFDS);
 
 	/* When virtualized, eIBRS could be hidden, assume vulnerable */
-	if (!(ia32_cap & ARCH_CAP_BHI_NO) &&
+	if (!(x86_arch_cap_msr & ARCH_CAP_BHI_NO) &&
 	    !cpu_matches(cpu_vuln_whitelist, NO_BHI) &&
 	    (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED) ||
 	     boot_cpu_has(X86_FEATURE_HYPERVISOR)))
···
 		return;
 
 	/* Rogue Data Cache Load? No! */
-	if (ia32_cap & ARCH_CAP_RDCL_NO)
+	if (x86_arch_cap_msr & ARCH_CAP_RDCL_NO)
 		return;
 
 	setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);

arch/x86/kernel/cpu/topology.c

···
 	early_per_cpu(x86_cpu_to_apicid, cpu) = apic_id;
 	early_per_cpu(x86_cpu_to_acpiid, cpu) = acpi_id;
 #endif
-	set_cpu_possible(cpu, true);
 	set_cpu_present(cpu, true);
 }
 
···
 		topo_info.nr_disabled_cpus++;
 	}
 
-	/* Register present and possible CPUs in the domain maps */
+	/*
+	 * Register present and possible CPUs in the domain
+	 * maps. cpu_possible_map will be updated in
+	 * topology_init_possible_cpus() after enumeration is done.
+	 */
 	for (dom = TOPO_SMT_DOMAIN; dom < TOPO_MAX_DOMAIN; dom++)
 		set_bit(topo_apicid(apic_id, dom), apic_maps[dom].map);
 }

arch/x86/kernel/cpu/topology_amd.c

···
 	if (!sft)
 		sft = get_count_order(ecx.cpu_nthreads + 1);
 
-	topology_set_dom(tscan, TOPO_SMT_DOMAIN, sft, ecx.cpu_nthreads + 1);
+	/*
+	 * cpu_nthreads describes the number of threads in the package
+	 * sft is the number of APIC ID bits per package
+	 *
+	 * As the number of actual threads per core is not described in
+	 * this leaf, just set the CORE domain shift and let the later
+	 * parsers set SMT shift. Assume one thread per core by default
+	 * which is correct if there are no other CPUID leafs to parse.
+	 */
+	topology_update_dom(tscan, TOPO_SMT_DOMAIN, 0, 1);
+	topology_set_dom(tscan, TOPO_CORE_DOMAIN, sft, ecx.cpu_nthreads + 1);
 	return true;
 }
 
-static void store_node(struct topo_scan *tscan, unsigned int nr_nodes, u16 node_id)
+static void store_node(struct topo_scan *tscan, u16 nr_nodes, u16 node_id)
 {
 	/*
 	 * Starting with Fam 17h the DIE domain could probably be used to
···
 	tscan->c->topo.initial_apicid = leaf.ext_apic_id;
 
 	/*
-	 * If leaf 0xb is available, then SMT shift is set already. If not
-	 * take it from ecx.threads_per_core and use topo_update_dom() -
-	 * topology_set_dom() would propagate and overwrite the already
-	 * propagated CORE level.
+	 * If leaf 0xb is available, then the domain shifts are set
+	 * already and nothing to do here.
 	 */
 	if (!has_0xb) {
+		/*
+		 * Leaf 0x80000008 set the CORE domain shift already.
+		 * Update the SMT domain, but do not propagate it.
+		 */
 		unsigned int nthreads = leaf.core_nthreads + 1;
 
 		topology_update_dom(tscan, TOPO_SMT_DOMAIN, get_count_order(nthreads), nthreads);
···
 
 static bool parse_fam10h_node_id(struct topo_scan *tscan)
 {
-	struct {
-		union {
+	union {
+		struct {
 			u64	node_id		:  3,
 				nodes_per_pkg	:  3,
 				unused		: 58;
-			u64	msr;
 		};
+		u64		msr;
 	} nid;
 
 	if (!boot_cpu_has(X86_FEATURE_NODEID_MSR))
···
 
 	/* parse_8000_0008() set everything up except llc_id */
 	tscan->c->topo.llc_id = apicid >> tscan->dom_shifts[TOPO_CORE_DOMAIN];
+}
+
+static void topoext_fixup(struct topo_scan *tscan)
+{
+	struct cpuinfo_x86 *c = tscan->c;
+	u64 msrval;
+
+	/* Try to re-enable TopologyExtensions if switched off by BIOS */
+	if (cpu_has(c, X86_FEATURE_TOPOEXT) || c->x86_vendor != X86_VENDOR_AMD ||
+	    c->x86 != 0x15 || c->x86_model < 0x10 || c->x86_model > 0x6f)
+		return;
+
+	if (msr_set_bit(0xc0011005, 54) <= 0)
+		return;
+
+	rdmsrl(0xc0011005, msrval);
+	if (msrval & BIT_64(54)) {
+		set_cpu_cap(c, X86_FEATURE_TOPOEXT);
+		pr_info_once(FW_INFO "CPU: Re-enabling disabled Topology Extensions Support.\n");
+	}
 }
 
 static void parse_topology_amd(struct topo_scan *tscan)
···
 void cpu_parse_topology_amd(struct topo_scan *tscan)
 {
 	tscan->amd_nodes_per_pkg = 1;
+	topoext_fixup(tscan);
 	parse_topology_amd(tscan);
 
 	if (tscan->amd_nodes_per_pkg > 1)

kernel/cpu.c

···
 };
 
 static enum cpu_mitigations cpu_mitigations __ro_after_init =
-	CPU_MITIGATIONS_AUTO;
+	IS_ENABLED(CONFIG_SPECULATION_MITIGATIONS) ? CPU_MITIGATIONS_AUTO :
+						     CPU_MITIGATIONS_OFF;
 
 static int __init mitigations_parse_cmdline(char *arg)
 {