linux-kernel - [tip: x86/fpu] x86/kvm: Avoid looking up PKRU in XSAVE buffer

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Message-ID: <162448616821.395.11390575510895361251.tip-bot2@tip-bot2>
Date:   Wed, 23 Jun 2021 22:09:28 -0000
From:   "tip-bot2 for Dave Hansen" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] x86/kvm: Avoid looking up PKRU in XSAVE buffer

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     71ef453355a9197fcfd8ff22391a4ad7861d79e6
Gitweb:        https://git.kernel.org/tip/71ef453355a9197fcfd8ff22391a4ad7861d79e6
Author:        Dave Hansen <dave.hansen@...ux.intel.com>
AuthorDate:    Wed, 23 Jun 2021 14:01:49 +02:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Wed, 23 Jun 2021 17:49:47 +02:00

x86/kvm: Avoid looking up PKRU in XSAVE buffer

PKRU is being removed from the kernel XSAVE/FPU buffers.  This removal
will probably include warnings for code that look up PKRU in those
buffers.

KVM currently looks up the location of PKRU but doesn't even use the
pointer that it gets back.  Rework the code to avoid calling
get_xsave_addr() except in cases where its result is actually used.

This makes the code more clear and also avoids the inevitable PKRU
warnings.

This is probably a good cleanup and could go upstream idependently
of any PKRU rework.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Borislav Petkov <bp@...e.de>
Link: https://lkml.kernel.org/r/20210623121453.541037562@linutronix.de
---
 arch/x86/kvm/x86.c | 45 ++++++++++++++++++++++++---------------------
 1 file changed, 24 insertions(+), 21 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index e0f4a46..c25bf24 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4604,20 +4604,21 @@ static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
 	 */
 	valid = xstate_bv & ~XFEATURE_MASK_FPSSE;
 	while (valid) {
+		u32 size, offset, ecx, edx;
 		u64 xfeature_mask = valid & -valid;
 		int xfeature_nr = fls64(xfeature_mask) - 1;
-		void *src = get_xsave_addr(xsave, xfeature_nr);
-
-		if (src) {
-			u32 size, offset, ecx, edx;
-			cpuid_count(XSTATE_CPUID, xfeature_nr,
-				    &size, &offset, &ecx, &edx);
-			if (xfeature_nr == XFEATURE_PKRU)
-				memcpy(dest + offset, &vcpu->arch.pkru,
-				       sizeof(vcpu->arch.pkru));
-			else
-				memcpy(dest + offset, src, size);
+		void *src;
+
+		cpuid_count(XSTATE_CPUID, xfeature_nr,
+			    &size, &offset, &ecx, &edx);
 
+		if (xfeature_nr == XFEATURE_PKRU) {
+			memcpy(dest + offset, &vcpu->arch.pkru,
+			       sizeof(vcpu->arch.pkru));
+		} else {
+			src = get_xsave_addr(xsave, xfeature_nr);
+			if (src)
+				memcpy(dest + offset, src, size);
 		}
 
 		valid -= xfeature_mask;
@@ -4647,18 +4648,20 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
 	 */
 	valid = xstate_bv & ~XFEATURE_MASK_FPSSE;
 	while (valid) {
+		u32 size, offset, ecx, edx;
 		u64 xfeature_mask = valid & -valid;
 		int xfeature_nr = fls64(xfeature_mask) - 1;
-		void *dest = get_xsave_addr(xsave, xfeature_nr);
-
-		if (dest) {
-			u32 size, offset, ecx, edx;
-			cpuid_count(XSTATE_CPUID, xfeature_nr,
-				    &size, &offset, &ecx, &edx);
-			if (xfeature_nr == XFEATURE_PKRU)
-				memcpy(&vcpu->arch.pkru, src + offset,
-				       sizeof(vcpu->arch.pkru));
-			else
+
+		cpuid_count(XSTATE_CPUID, xfeature_nr,
+			    &size, &offset, &ecx, &edx);
+
+		if (xfeature_nr == XFEATURE_PKRU) {
+			memcpy(&vcpu->arch.pkru, src + offset,
+			       sizeof(vcpu->arch.pkru));
+		} else {
+			void *dest = get_xsave_addr(xsave, xfeature_nr);
+
+			if (dest)
 				memcpy(dest, src + offset, size);
 		}