[RFC PATCH v4 04/18] arm64: Introduce por_elx_set_pkey_perms() helper

[Kevin Brodsky <kevin.brodsky@arm.com>]

Introduce a helper that sets the permissions of a given pkey
(POIndex) in the POR_ELx format, and make use of it in
arch_set_user_pkey_access().

Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
 arch/arm64/include/asm/por.h |  7 +++++++
 arch/arm64/mm/mmu.c          | 26 ++++++++++----------------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/arch/arm64/include/asm/por.h b/arch/arm64/include/asm/por.h
index d913d5b529e4..bffb4d2b1246 100644
--- a/arch/arm64/include/asm/por.h
+++ b/arch/arm64/include/asm/por.h
@@ -31,4 +31,11 @@ static inline bool por_elx_allows_exec(u64 por, u8 pkey)
 	return perm & POE_X;
 }
 
+static inline u64 por_elx_set_pkey_perms(u64 por, u8 pkey, u64 perms)
+{
+	u64 shift = POR_ELx_PERM_SHIFT(pkey);
+
+	return (por & ~(POE_MASK << shift)) | (perms << shift);
+}
+
 #endif /* _ASM_ARM64_POR_H */
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 8fcf59ba39db..89a331e699d2 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1578,8 +1578,8 @@ void __cpu_replace_ttbr1(pgd_t *pgdp, bool cnp)
 #ifdef CONFIG_ARCH_HAS_PKEYS
 int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long init_val)
 {
-	u64 new_por;
-	u64 old_por;
+	u64 new_perms;
+	u64 por;
 
 	if (!system_supports_poe())
 		return -ENOSPC;
@@ -1593,25 +1593,19 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, unsigned long i
 		return -EINVAL;
 
 	/* Set the bits we need in POR:  */
-	new_por = POE_RWX;
+	new_perms = POE_RWX;
 	if (init_val & PKEY_DISABLE_WRITE)
-		new_por &= ~POE_W;
+		new_perms &= ~POE_W;
 	if (init_val & PKEY_DISABLE_ACCESS)
-		new_por &= ~POE_RW;
+		new_perms &= ~POE_RW;
 	if (init_val & PKEY_DISABLE_READ)
-		new_por &= ~POE_R;
+		new_perms &= ~POE_R;
 	if (init_val & PKEY_DISABLE_EXECUTE)
-		new_por &= ~POE_X;
+		new_perms &= ~POE_X;
 
-	/* Shift the bits in to the correct place in POR for pkey: */
-	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 << POR_ELx_PERM_SHIFT(pkey));
-
-	/* Write old part along with new part: */
-	write_sysreg_s(old_por | new_por, SYS_POR_EL0);
+	por = read_sysreg_s(SYS_POR_EL0);
+	por = por_elx_set_pkey_perms(por, pkey, new_perms);
+	write_sysreg_s(por, SYS_POR_EL0);
 
 	return 0;
 }
-- 
2.47.0