[PATCH v13 7/8] KVM: arm64: use CASLT instruction for swapping guest descriptor

[Yeoreum Yun <yeoreum.yun@arm.com>]

Use the CASLT instruction to swap the guest descriptor when FEAT_LSUI
is enabled, avoiding the need to clear the PAN bit.

Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
---
 arch/arm64/include/asm/futex.h | 17 +----------------
 arch/arm64/include/asm/lsui.h  | 27 +++++++++++++++++++++++++++
 arch/arm64/kvm/at.c            | 32 +++++++++++++++++++++++++++++++-
 3 files changed, 59 insertions(+), 17 deletions(-)
 create mode 100644 arch/arm64/include/asm/lsui.h

diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
index b579e9d0964d..6779c4ad927f 100644
--- a/arch/arm64/include/asm/futex.h
+++ b/arch/arm64/include/asm/futex.h
@@ -7,11 +7,9 @@
 
 #include <linux/futex.h>
 #include <linux/uaccess.h>
-#include <linux/stringify.h>
 
-#include <asm/alternative.h>
-#include <asm/alternative-macros.h>
 #include <asm/errno.h>
+#include <asm/lsui.h>
 
 #define FUTEX_MAX_LOOPS	128 /* What's the largest number you can think of? */
 
@@ -91,8 +89,6 @@ __llsc_futex_cmpxchg(u32 __user *uaddr, u32 oldval, u32 newval, u32 *oval)
 
 #ifdef CONFIG_ARM64_LSUI
 
-#define __LSUI_PREAMBLE	".arch_extension lsui\n"
-
 #define LSUI_FUTEX_ATOMIC_OP(op, asm_op)				\
 static __always_inline int						\
 __lsui_futex_atomic_##op(int oparg, u32 __user *uaddr, int *oval)	\
@@ -235,17 +231,6 @@ __lsui_futex_cmpxchg(u32 __user *uaddr, u32 oldval, u32 newval, u32 *oval)
 {
 	return __lsui_cmpxchg32(uaddr, oldval, newval, oval);
 }
-
-#define __lsui_llsc_body(op, ...)					\
-({									\
-	alternative_has_cap_unlikely(ARM64_HAS_LSUI) ?			\
-		__lsui_##op(__VA_ARGS__) : __llsc_##op(__VA_ARGS__);	\
-})
-
-#else	/* CONFIG_ARM64_LSUI */
-
-#define __lsui_llsc_body(op, ...)	__llsc_##op(__VA_ARGS__)
-
 #endif	/* CONFIG_ARM64_LSUI */
 
 
diff --git a/arch/arm64/include/asm/lsui.h b/arch/arm64/include/asm/lsui.h
new file mode 100644
index 000000000000..4f956188835e
--- /dev/null
+++ b/arch/arm64/include/asm/lsui.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_LSUI_H
+#define __ASM_LSUI_H
+
+#include <linux/compiler_types.h>
+#include <linux/stringify.h>
+#include <asm/alternative.h>
+#include <asm/alternative-macros.h>
+#include <asm/cpucaps.h>
+
+#ifdef CONFIG_ARM64_LSUI
+
+#define __LSUI_PREAMBLE	".arch_extension lsui\n"
+
+#define __lsui_llsc_body(op, ...)					\
+({									\
+	alternative_has_cap_unlikely(ARM64_HAS_LSUI) ?			\
+		__lsui_##op(__VA_ARGS__) : __llsc_##op(__VA_ARGS__);	\
+})
+
+#else	/* CONFIG_ARM64_LSUI */
+
+#define __lsui_llsc_body(op, ...)	__llsc_##op(__VA_ARGS__)
+
+#endif	/* CONFIG_ARM64_LSUI */
+
+#endif	/* __ASM_LSUI_H */
diff --git a/arch/arm64/kvm/at.c b/arch/arm64/kvm/at.c
index 885bd5bb2f41..1aceeef04567 100644
--- a/arch/arm64/kvm/at.c
+++ b/arch/arm64/kvm/at.c
@@ -9,6 +9,7 @@
 #include <asm/esr.h>
 #include <asm/kvm_hyp.h>
 #include <asm/kvm_mmu.h>
+#include <asm/lsui.h>
 
 static void fail_s1_walk(struct s1_walk_result *wr, u8 fst, bool s1ptw)
 {
@@ -1704,6 +1705,33 @@ int __kvm_find_s1_desc_level(struct kvm_vcpu *vcpu, u64 va, u64 ipa, int *level)
 	}
 }
 
+#ifdef CONFIG_ARM64_LSUI
+static int __lsui_swap_desc(u64 __user *ptep, u64 old, u64 new)
+{
+	u64 tmp = old;
+	int ret = 0;
+
+	uaccess_ttbr0_enable();
+
+	asm volatile(__LSUI_PREAMBLE
+		     "1: caslt	%[old], %[new], %[addr]\n"
+		     "2:\n"
+		     _ASM_EXTABLE_UACCESS_ERR(1b, 2b, %w[ret])
+		     : [old] "+r" (old), [addr] "+Q" (*ptep), [ret] "+r" (ret)
+		     : [new] "r" (new)
+		     : "memory");
+
+	uaccess_ttbr0_disable();
+
+	if (ret)
+		return ret;
+	if (tmp != old)
+		return -EAGAIN;
+
+	return ret;
+}
+#endif
+
 static int __lse_swap_desc(u64 __user *ptep, u64 old, u64 new)
 {
 	u64 tmp = old;
@@ -1779,7 +1807,9 @@ int __kvm_at_swap_desc(struct kvm *kvm, gpa_t ipa, u64 old, u64 new)
 		return -EPERM;
 
 	ptep = (u64 __user *)hva + offset;
-	if (cpus_have_final_cap(ARM64_HAS_LSE_ATOMICS))
+	if (IS_ENABLED(CONFIG_ARM64_LSUI) && cpus_have_final_cap(ARM64_HAS_LSUI))
+		r = __lsui_swap_desc(ptep, old, new);
+	else if (cpus_have_final_cap(ARM64_HAS_LSE_ATOMICS))
 		r = __lse_swap_desc(ptep, old, new);
 	else
 		r = __llsc_swap_desc(ptep, old, new);
-- 
LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}