arm64/sysreg: Improve PIR/POR helpers

We currently have one helper to set a PIRx_ELx's permission field to
a given value, PIRx_ELx_PERM(), and another helper to extract a
permission field from POR_ELx, POR_ELx_IDX(). The naming is pretty
confusing - it isn't clear at all that "_PERM" corresponds to a
setter and "_IDX" to a getter.

This patch aims at improving the situation by using the same
suffixes as FIELD_PREP()/FIELD_GET(), which we have already adopted
for SYS_FIELD_{PREP,GET}():

* PIRx_ELx_PERM_PREP(), POR_ELx_PERM_PREP() create a register value
where the permission field for a given index is set to a given value.

* POR_ELx_PERM_GET() extracts the permission field from a given
register value for a given index.

These helpers are not implemented using FIELD_PREP()/FIELD_GET()
because the mask may not be constant, and they need to be usable in
assembly. They are all defined in asm/sysreg.h, as one would expect
for basic sysreg-related helpers.

Finally the new POR_ELx_PERM_* macros are used for existing
calculations in signal.c and mmu.c.

Signed-off-by: Kevin Brodsky <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Catalin Marinas <[e-mail]>

arch/arm64/include/asm/pgtable-prot.h

···
 #define PAGE_GCS_RO	__pgprot(_PAGE_GCS_RO)
 
 #define PIE_E0	( \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS),           PIE_GCS)  | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS_RO),        PIE_R)   | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_EXECONLY),      PIE_X_O) | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY_EXEC), PIE_RX_O)  | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED_EXEC),   PIE_RWX_O) | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY),      PIE_R_O)   | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED),        PIE_RW_O))
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS),           PIE_GCS)  | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS_RO),        PIE_R)   | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_EXECONLY),      PIE_X_O) | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_READONLY_EXEC), PIE_RX_O)  | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED_EXEC),   PIE_RWX_O) | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_READONLY),      PIE_R_O)   | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED),        PIE_RW_O))
 
 #define PIE_E1	( \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS),           PIE_NONE_O) | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_GCS_RO),        PIE_NONE_O) | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_EXECONLY),      PIE_NONE_O) | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY_EXEC), PIE_R)      | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED_EXEC),   PIE_RW)     | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_READONLY),      PIE_R)      | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_SHARED),        PIE_RW)     | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_KERNEL_ROX),    PIE_RX)     | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_KERNEL_EXEC),   PIE_RWX)    | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_KERNEL_RO),     PIE_R)      | \
-	PIRx_ELx_PERM(pte_pi_index(_PAGE_KERNEL),        PIE_RW))
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS),           PIE_NONE_O) | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_GCS_RO),        PIE_NONE_O) | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_EXECONLY),      PIE_NONE_O) | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_READONLY_EXEC), PIE_R)      | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED_EXEC),   PIE_RW)     | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_READONLY),      PIE_R)      | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_SHARED),        PIE_RW)     | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_ROX),    PIE_RX)     | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_EXEC),   PIE_RWX)    | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL_RO),     PIE_R)      | \
+	PIRx_ELx_PERM_PREP(pte_pi_index(_PAGE_KERNEL),        PIE_RW))
 
 #endif /* __ASM_PGTABLE_PROT_H */

arch/arm64/include/asm/por.h

···
 #ifndef _ASM_ARM64_POR_H
 #define _ASM_ARM64_POR_H
 
-#define POR_BITS_PER_PKEY		4
-#define POR_ELx_IDX(por_elx, idx)	(((por_elx) >> ((idx) * POR_BITS_PER_PKEY)) & 0xf)
+#include <asm/sysreg.h>
 
 static inline bool por_elx_allows_read(u64 por, u8 pkey)
 {
-	u8 perm = POR_ELx_IDX(por, pkey);
+	u8 perm = POR_ELx_PERM_GET(pkey, por);
 
 	return perm & POE_R;
 }
 
 static inline bool por_elx_allows_write(u64 por, u8 pkey)
 {
-	u8 perm = POR_ELx_IDX(por, pkey);
+	u8 perm = POR_ELx_PERM_GET(pkey, por);
 
 	return perm & POE_W;
 }
 
 static inline bool por_elx_allows_exec(u64 por, u8 pkey)
 {
-	u8 perm = POR_ELx_IDX(por, pkey);
+	u8 perm = POR_ELx_PERM_GET(pkey, por);
 
 	return perm & POE_X;
 }

arch/arm64/include/asm/sysreg.h

···
 #define PIE_RX		UL(0xa)
 #define PIE_RW		UL(0xc)
 #define PIE_RWX		UL(0xe)
+#define PIE_MASK	UL(0xf)
 
-#define PIRx_ELx_PERM(idx, perm)	((perm) << ((idx) * 4))
+#define PIRx_ELx_BITS_PER_IDX		4
+#define PIRx_ELx_PERM_SHIFT(idx)	((idx) * PIRx_ELx_BITS_PER_IDX)
+#define PIRx_ELx_PERM_PREP(idx, perm)	(((perm) & PIE_MASK) << PIRx_ELx_PERM_SHIFT(idx))
 
 /*
  * Permission Overlay Extension (POE) permission encodings.
···
 #define POE_XW		UL(0x6)
 #define POE_RXW		UL(0x7)
 #define POE_MASK	UL(0xf)
+
+#define POR_ELx_BITS_PER_IDX		4
+#define POR_ELx_PERM_SHIFT(idx)		((idx) * POR_ELx_BITS_PER_IDX)
+#define POR_ELx_PERM_GET(idx, reg)	(((reg) >> POR_ELx_PERM_SHIFT(idx)) & POE_MASK)
+#define POR_ELx_PERM_PREP(idx, perm)	(((perm) & POE_MASK) << POR_ELx_PERM_SHIFT(idx))
 
 /* Initial value for Permission Overlay Extension for EL0 */
 #define POR_EL0_INIT	POE_RXW

arch/arm64/kernel/signal.c

···
 		u64 por_enable_all = 0;
 
 		for (int pkey = 0; pkey < arch_max_pkey(); pkey++)
-			por_enable_all |= POE_RXW << (pkey * POR_BITS_PER_PKEY);
+			por_enable_all |= POR_ELx_PERM_PREP(pkey, POE_RXW);
 
 		ua_state->por_el0 = read_sysreg_s(SYS_POR_EL0);
 		write_sysreg_s(por_enable_all, SYS_POR_EL0);

arch/arm64/mm/mmu.c

···
 {
 	u64 new_por = POE_RXW;
 	u64 old_por;
-	u64 pkey_shift;
 
 	if (!system_supports_poe())
 		return -ENOSPC;
···
 		new_por &= ~POE_X;
 
 	/* Shift the bits in to the correct place in POR for pkey: */
-	pkey_shift = pkey * POR_BITS_PER_PKEY;
-	new_por <<= pkey_shift;
+	new_por = POR_ELx_PERM_PREP(pkey, new_por);
 
 	/* Get old POR and mask off any old bits in place: */
 	old_por = read_sysreg_s(SYS_POR_EL0);
-	old_por &= ~(POE_MASK << pkey_shift);
+	old_por &= ~(POE_MASK << POR_ELx_PERM_SHIFT(pkey));
 
 	/* Write old part along with new part: */
 	write_sysreg_s(old_por | new_por, SYS_POR_EL0);