[PATCH v4 06/21] x86/fpu: Ignore APX when copying from/to guest FPU

[Chang S. Bae]

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

KVM will store APX extended GPRs directly in the regs[] field of struct
kvm_vcpu.  This is done to make accessors more uniform between GPRs and
EGPRs, and partly because x86 maintainers expressed the desire to compile
Linux with APX enabled sooner or later; accessing guest EGPRs from KVM's
C code would get in the way.

Therefore, let KVM handle the APX feature on its own when executing
ioctls to get and set the virtual machine's XSAVE state.

Cc: x86@xxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[ chang: adjust function prototype ]
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
---
V3 -> V4: New patch
---
 arch/x86/include/asm/fpu/api.h | 2 +-
 arch/x86/kernel/fpu/core.c     | 9 +++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h
index cd6f194a912b..0b218f5eaafd 100644
--- a/arch/x86/include/asm/fpu/api.h
+++ b/arch/x86/include/asm/fpu/api.h
@@ -160,7 +160,7 @@ static inline void fpu_sync_guest_vmexit_xfd_state(void) { }
 
 extern void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
 					   unsigned int size, u64 xfeatures, u32 pkru);
-extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf, u64 xcr0, u32 *vpkru);
+extern int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, void *buf, u64 xcr0, u32 *vpkru);
 
 static inline void fpstate_set_confidential(struct fpu_guest *gfpu)
 {
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 608983806fd7..ae5c73faed69 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -420,6 +420,8 @@ void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
 	struct membuf mb = { .p = buf, .left = size };
 
 	if (cpu_feature_enabled(X86_FEATURE_XSAVE)) {
+		/* Up to date APX registers are in struct kvm_vcpu anyway.  */
+		xfeatures &= ~XFEATURE_MASK_APX;
 		__copy_xstate_to_uabi_buf(mb, kstate, xfeatures, pkru,
 					  XSTATE_COPY_XSAVE);
 	} else {
@@ -431,11 +433,11 @@ void fpu_copy_guest_fpstate_to_uabi(struct fpu_guest *gfpu, void *buf,
 }
 EXPORT_SYMBOL_FOR_KVM(fpu_copy_guest_fpstate_to_uabi);
 
-int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
+int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, void *buf,
 				   u64 xcr0, u32 *vpkru)
 {
 	struct fpstate *kstate = gfpu->fpstate;
-	const union fpregs_state *ustate = buf;
+	union fpregs_state *ustate = buf;
 
 	if (!cpu_feature_enabled(X86_FEATURE_XSAVE)) {
 		if (ustate->xsave.header.xfeatures & ~XFEATURE_MASK_FPSSE)
@@ -464,6 +466,9 @@ int fpu_copy_uabi_to_guest_fpstate(struct fpu_guest *gfpu, const void *buf,
 	if (!(ustate->xsave.header.xfeatures & XFEATURE_MASK_PKRU))
 		vpkru = NULL;
 
+	/* APX registers are copied to and from struct kvm_vcpu, not the FPU.  */
+	ustate->xsave.header.xfeatures &= ~XFEATURE_MASK_APX;
+
 	return copy_uabi_from_kernel_to_xstate(kstate, ustate, vpkru);
 }
 EXPORT_SYMBOL_FOR_KVM(fpu_copy_uabi_to_guest_fpstate);
-- 
2.51.0