x86/boot: Port I/O: Add decompression-time support for TDX

Port I/O instructions trigger #VE in the TDX environment. In response to
the exception, kernel emulates these instructions using hypercalls.

But during early boot, on the decompression stage, it is cumbersome to
deal with #VE. It is cleaner to go to hypercalls directly, bypassing #VE
handling.

Hook up TDX-specific port I/O helpers if booting in TDX environment.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Signed-off-by: Dave Hansen <[e-mail]>
Reviewed-by: Dave Hansen <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/boot/compressed/Makefile

···
 endif
 
 vmlinux-objs-$(CONFIG_ACPI) += $(obj)/acpi.o
-vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o
+vmlinux-objs-$(CONFIG_INTEL_TDX_GUEST) += $(obj)/tdx.o $(obj)/tdcall.o
 
 vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_thunk_$(BITS).o
 efi-obj-$(CONFIG_EFI_STUB) = $(objtree)/drivers/firmware/efi/libstub/lib.a

arch/x86/boot/compressed/tdcall.S

···
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#include "../../coco/tdx/tdcall.S"

arch/x86/boot/compressed/tdx.c

···
 
 #include "../cpuflags.h"
 #include "../string.h"
+#include "../io.h"
+#include "error.h"
+
+#include <vdso/limits.h>
+#include <uapi/asm/vmx.h>
 
 #include <asm/shared/tdx.h>
+
+/* Called from __tdx_hypercall() for unrecoverable failure */
+void __tdx_hypercall_failed(void)
+{
+	error("TDVMCALL failed. TDX module bug?");
+}
+
+static inline unsigned int tdx_io_in(int size, u16 port)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = EXIT_REASON_IO_INSTRUCTION,
+		.r12 = size,
+		.r13 = 0,
+		.r14 = port,
+	};
+
+	if (__tdx_hypercall(&args, TDX_HCALL_HAS_OUTPUT))
+		return UINT_MAX;
+
+	return args.r11;
+}
+
+static inline void tdx_io_out(int size, u16 port, u32 value)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = EXIT_REASON_IO_INSTRUCTION,
+		.r12 = size,
+		.r13 = 1,
+		.r14 = port,
+		.r15 = value,
+	};
+
+	__tdx_hypercall(&args, 0);
+}
+
+static inline u8 tdx_inb(u16 port)
+{
+	return tdx_io_in(1, port);
+}
+
+static inline void tdx_outb(u8 value, u16 port)
+{
+	tdx_io_out(1, port, value);
+}
+
+static inline void tdx_outw(u16 value, u16 port)
+{
+	tdx_io_out(2, port, value);
+}
 
 void early_tdx_detect(void)
 {
···
 
 	if (memcmp(TDX_IDENT, sig, sizeof(sig)))
 		return;
+
+	/* Use hypercalls instead of I/O instructions */
+	pio_ops.f_inb  = tdx_inb;
+	pio_ops.f_outb = tdx_outb;
+	pio_ops.f_outw = tdx_outw;
 }

arch/x86/include/asm/shared/tdx.h

···
 #ifndef _ASM_X86_SHARED_TDX_H
 #define _ASM_X86_SHARED_TDX_H
 
+#include <linux/bits.h>
+#include <linux/types.h>
+
+#define TDX_HYPERCALL_STANDARD  0
+
+#define TDX_HCALL_HAS_OUTPUT	BIT(0)
+#define TDX_HCALL_ISSUE_STI	BIT(1)
+
 #define TDX_CPUID_LEAF_ID	0x21
 #define TDX_IDENT		"IntelTDX    "
 
+#ifndef __ASSEMBLY__
+
+/*
+ * Used in __tdx_hypercall() to pass down and get back registers' values of
+ * the TDCALL instruction when requesting services from the VMM.
+ *
+ * This is a software only structure and not part of the TDX module/VMM ABI.
+ */
+struct tdx_hypercall_args {
+	u64 r10;
+	u64 r11;
+	u64 r12;
+	u64 r13;
+	u64 r14;
+	u64 r15;
+};
+
+/* Used to request services from the VMM */
+u64 __tdx_hypercall(struct tdx_hypercall_args *args, unsigned long flags);
+
+/* Called from __tdx_hypercall() for unrecoverable failure */
+void __tdx_hypercall_failed(void);
+
+#endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_SHARED_TDX_H */

arch/x86/include/asm/tdx.h

···
 #ifndef _ASM_X86_TDX_H
 #define _ASM_X86_TDX_H
 
-#include <linux/bits.h>
 #include <linux/init.h>
 #include <linux/bits.h>
 #include <asm/ptrace.h>
 #include <asm/shared/tdx.h>
-
-#define TDX_HYPERCALL_STANDARD  0
-
-#define TDX_HCALL_HAS_OUTPUT	BIT(0)
-#define TDX_HCALL_ISSUE_STI	BIT(1)
 
 /*
  * SW-defined error codes.
···
 };
 
 /*
- * Used in __tdx_hypercall() to pass down and get back registers' values of
- * the TDCALL instruction when requesting services from the VMM.
- *
- * This is a software only structure and not part of the TDX module/VMM ABI.
- */
-struct tdx_hypercall_args {
-	u64 r10;
-	u64 r11;
-	u64 r12;
-	u64 r13;
-	u64 r14;
-	u64 r15;
-};
-
-/*
  * Used by the #VE exception handler to gather the #VE exception
  * info from the TDX module. This is a software only structure
  * and not part of the TDX module/VMM ABI.
···
 /* Used to communicate with the TDX module */
 u64 __tdx_module_call(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
 		      struct tdx_module_output *out);
-
-/* Used to request services from the VMM */
-u64 __tdx_hypercall(struct tdx_hypercall_args *args, unsigned long flags);
-
-/* Called from __tdx_hypercall() for unrecoverable failure */
-void __tdx_hypercall_failed(void);
 
 void tdx_get_ve_info(struct ve_info *ve);