* [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS
@ 2025-11-06 10:11 Binbin Wu
2025-11-07 3:14 ` Chao Gao
0 siblings, 1 reply; 5+ messages in thread
From: Binbin Wu @ 2025-11-06 10:11 UTC (permalink / raw)
To: seanjc, pbonzini; +Cc: kvm, linux-kernel, binbin.wu
Add and use a helper, kvm_load_xfeatures(), to dedup the code that loads
guest/host xfeatures by passing XCR0 and XSS values accordingly.
No functional change intended.
Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
---
The patch is based on the patch series
"KVM: x86: Cleanup #MC and XCR0/XSS/PKRU handling" [1], which is applied on
top of kvm-x86 next branch(commit a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a).
[1] https://lore.kernel.org/all/20251030224246.3456492-1-seanjc@google.com
---
arch/x86/kvm/x86.c | 25 +++++--------------------
1 file changed, 5 insertions(+), 20 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b8df02a083b2..35fc1333e198 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1203,33 +1203,18 @@ void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_lmsw);
-static void kvm_load_guest_xfeatures(struct kvm_vcpu *vcpu)
+static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, u64 xcr0, u64 xss)
{
if (vcpu->arch.guest_state_protected)
return;
if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
if (vcpu->arch.xcr0 != kvm_host.xcr0)
- xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
+ xsetbv(XCR_XFEATURE_ENABLED_MASK, xcr0);
if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
vcpu->arch.ia32_xss != kvm_host.xss)
- wrmsrq(MSR_IA32_XSS, vcpu->arch.ia32_xss);
- }
-}
-
-static void kvm_load_host_xfeatures(struct kvm_vcpu *vcpu)
-{
- if (vcpu->arch.guest_state_protected)
- return;
-
- if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
- if (vcpu->arch.xcr0 != kvm_host.xcr0)
- xsetbv(XCR_XFEATURE_ENABLED_MASK, kvm_host.xcr0);
-
- if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
- vcpu->arch.ia32_xss != kvm_host.xss)
- wrmsrq(MSR_IA32_XSS, kvm_host.xss);
+ wrmsrq(MSR_IA32_XSS, xss);
}
}
@@ -11310,7 +11295,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
if (vcpu->arch.guest_fpu.xfd_err)
wrmsrq(MSR_IA32_XFD_ERR, vcpu->arch.guest_fpu.xfd_err);
- kvm_load_guest_xfeatures(vcpu);
+ kvm_load_xfeatures(vcpu, vcpu->arch.xcr0, vcpu->arch.ia32_xss);
if (unlikely(vcpu->arch.switch_db_regs &&
!(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH))) {
@@ -11406,7 +11391,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
vcpu->mode = OUTSIDE_GUEST_MODE;
smp_wmb();
- kvm_load_host_xfeatures(vcpu);
+ kvm_load_xfeatures(vcpu, kvm_host.xcr0, kvm_host.xss);
/*
* Sync xfd before calling handle_exit_irqoff() which may
base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a
prerequisite-patch-id: 9aafd634f0ab2033d7b032e227d356777469e046
prerequisite-patch-id: 656ce1f5aa97c77a9cf6125713707a5007b2c7ba
prerequisite-patch-id: d6328b8c0fdb8593bb534ab7378821edcf9f639d
prerequisite-patch-id: c7f36d1cedc4ae6416223d2225460944629b3d4f
--
2.46.0
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS
2025-11-06 10:11 [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS Binbin Wu
@ 2025-11-07 3:14 ` Chao Gao
2025-11-07 4:21 ` Binbin Wu
2025-11-07 6:17 ` Xiaoyao Li
0 siblings, 2 replies; 5+ messages in thread
From: Chao Gao @ 2025-11-07 3:14 UTC (permalink / raw)
To: Binbin Wu; +Cc: seanjc, pbonzini, kvm, linux-kernel
s/help/helper in the subject.
On Thu, Nov 06, 2025 at 06:11:38PM +0800, Binbin Wu wrote:
>Add and use a helper, kvm_load_xfeatures(), to dedup the code that loads
>guest/host xfeatures by passing XCR0 and XSS values accordingly.
>
>No functional change intended.
>
>Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
<snip>
>@@ -11406,7 +11391,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> vcpu->mode = OUTSIDE_GUEST_MODE;
> smp_wmb();
>
>- kvm_load_host_xfeatures(vcpu);
>+ kvm_load_xfeatures(vcpu, kvm_host.xcr0, kvm_host.xss);
Nit: given that xcr0/xss are either guest or host values, would it be slightly
better for this helper to accept a boolean (e.g., bool load_guest) to convey
that the API loads guest (or host) values rather than arbitrary xcr0/xss
values? like fpu_swap_kvm_fpstate().
static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
{
u64 xcr0 = load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0;
u64 xss = load_guest ? vcpu->arch.ia32_xss : kvm_host.xss;
if (vcpu->arch.guest_state_protected)
return;
> /*
> * Sync xfd before calling handle_exit_irqoff() which may
>
>base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a
>prerequisite-patch-id: 9aafd634f0ab2033d7b032e227d356777469e046
>prerequisite-patch-id: 656ce1f5aa97c77a9cf6125713707a5007b2c7ba
>prerequisite-patch-id: d6328b8c0fdb8593bb534ab7378821edcf9f639d
>prerequisite-patch-id: c7f36d1cedc4ae6416223d2225460944629b3d4f
>--
>2.46.0
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS
2025-11-07 3:14 ` Chao Gao
@ 2025-11-07 4:21 ` Binbin Wu
2025-11-07 19:09 ` Sean Christopherson
2025-11-07 6:17 ` Xiaoyao Li
1 sibling, 1 reply; 5+ messages in thread
From: Binbin Wu @ 2025-11-07 4:21 UTC (permalink / raw)
To: Chao Gao; +Cc: seanjc, pbonzini, kvm, linux-kernel
On 11/7/2025 11:14 AM, Chao Gao wrote:
> s/help/helper in the subject.
>
> On Thu, Nov 06, 2025 at 06:11:38PM +0800, Binbin Wu wrote:
>> Add and use a helper, kvm_load_xfeatures(), to dedup the code that loads
>> guest/host xfeatures by passing XCR0 and XSS values accordingly.
>>
>> No functional change intended.
>>
>> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
>
> <snip>
>
>> @@ -11406,7 +11391,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>> vcpu->mode = OUTSIDE_GUEST_MODE;
>> smp_wmb();
>>
>> - kvm_load_host_xfeatures(vcpu);
>> + kvm_load_xfeatures(vcpu, kvm_host.xcr0, kvm_host.xss);
> Nit: given that xcr0/xss are either guest or host values, would it be slightly
> better for this helper to accept a boolean (e.g., bool load_guest) to convey
> that the API loads guest (or host) values rather than arbitrary xcr0/xss
> values? like fpu_swap_kvm_fpstate().
Make sense.
>
> static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
> {
> u64 xcr0 = load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0;
> u64 xss = load_guest ? vcpu->arch.ia32_xss : kvm_host.xss;
Since they are only used once, I even want to open code them as:
static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
{
if (vcpu->arch.guest_state_protected)
return;
if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
if (vcpu->arch.xcr0 != kvm_host.xcr0)
xsetbv(XCR_XFEATURE_ENABLED_MASK,
load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0);
if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
vcpu->arch.ia32_xss != kvm_host.xss)
wrmsrq(MSR_IA32_XSS,
load_guest ? vcpu->arch.ia32_xss : kvm_host.xss);
}
}
>
> if (vcpu->arch.guest_state_protected)
> return;
>
>> /*
>> * Sync xfd before calling handle_exit_irqoff() which may
>>
>> base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a
>> prerequisite-patch-id: 9aafd634f0ab2033d7b032e227d356777469e046
>> prerequisite-patch-id: 656ce1f5aa97c77a9cf6125713707a5007b2c7ba
>> prerequisite-patch-id: d6328b8c0fdb8593bb534ab7378821edcf9f639d
>> prerequisite-patch-id: c7f36d1cedc4ae6416223d2225460944629b3d4f
>> --
>> 2.46.0
>>
>>
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS
2025-11-07 4:21 ` Binbin Wu
@ 2025-11-07 19:09 ` Sean Christopherson
0 siblings, 0 replies; 5+ messages in thread
From: Sean Christopherson @ 2025-11-07 19:09 UTC (permalink / raw)
To: Binbin Wu; +Cc: Chao Gao, pbonzini, kvm, linux-kernel
On Fri, Nov 07, 2025, Binbin Wu wrote:
>
>
> On 11/7/2025 11:14 AM, Chao Gao wrote:
> > s/help/helper in the subject.
> >
> > On Thu, Nov 06, 2025 at 06:11:38PM +0800, Binbin Wu wrote:
> > > Add and use a helper, kvm_load_xfeatures(), to dedup the code that loads
> > > guest/host xfeatures by passing XCR0 and XSS values accordingly.
> > >
> > > No functional change intended.
> > >
> > > Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
> > Reviewed-by: Chao Gao <chao.gao@intel.com>
> >
> > <snip>
> >
> > > @@ -11406,7 +11391,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> > > vcpu->mode = OUTSIDE_GUEST_MODE;
> > > smp_wmb();
> > >
> > > - kvm_load_host_xfeatures(vcpu);
> > > + kvm_load_xfeatures(vcpu, kvm_host.xcr0, kvm_host.xss);
> > Nit: given that xcr0/xss are either guest or host values, would it be slightly
> > better for this helper to accept a boolean (e.g., bool load_guest) to convey
> > that the API loads guest (or host) values rather than arbitrary xcr0/xss
> > values? like fpu_swap_kvm_fpstate().
>
> Make sense.
I don't love passing true/false, but I Xiaoyao does make a good a point that
subtly requiring the caller to pass vcpu->arch.xcr0 vs. kvm_host.xcr0 is weird
and confusing.
> > static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
> > {
> > u64 xcr0 = load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0;
> > u64 xss = load_guest ? vcpu->arch.ia32_xss : kvm_host.xss;
>
> Since they are only used once, I even want to open code them as:
+100, I find your version much more intuitive.
> static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
> {
> if (vcpu->arch.guest_state_protected)
> return;
>
> if (kvm_is_cr4_bit_set(vcpu, X86_CR4_OSXSAVE)) {
> if (vcpu->arch.xcr0 != kvm_host.xcr0)
> xsetbv(XCR_XFEATURE_ENABLED_MASK,
> load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0);
>
> if (guest_cpu_cap_has(vcpu, X86_FEATURE_XSAVES) &&
> vcpu->arch.ia32_xss != kvm_host.xss)
> wrmsrq(MSR_IA32_XSS,
> load_guest ? vcpu->arch.ia32_xss : kvm_host.xss);
> }
> }
>
> >
> > if (vcpu->arch.guest_state_protected)
> > return;
> >
> > > /*
> > > * Sync xfd before calling handle_exit_irqoff() which may
> > >
> > > base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a
> > > prerequisite-patch-id: 9aafd634f0ab2033d7b032e227d356777469e046
> > > prerequisite-patch-id: 656ce1f5aa97c77a9cf6125713707a5007b2c7ba
> > > prerequisite-patch-id: d6328b8c0fdb8593bb534ab7378821edcf9f639d
> > > prerequisite-patch-id: c7f36d1cedc4ae6416223d2225460944629b3d4f
> > > --
> > > 2.46.0
> > >
> > >
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS
2025-11-07 3:14 ` Chao Gao
2025-11-07 4:21 ` Binbin Wu
@ 2025-11-07 6:17 ` Xiaoyao Li
1 sibling, 0 replies; 5+ messages in thread
From: Xiaoyao Li @ 2025-11-07 6:17 UTC (permalink / raw)
To: Chao Gao, Binbin Wu; +Cc: seanjc, pbonzini, kvm, linux-kernel
On 11/7/2025 11:14 AM, Chao Gao wrote:
> s/help/helper in the subject.
>
> On Thu, Nov 06, 2025 at 06:11:38PM +0800, Binbin Wu wrote:
>> Add and use a helper, kvm_load_xfeatures(), to dedup the code that loads
>> guest/host xfeatures by passing XCR0 and XSS values accordingly.
>>
>> No functional change intended.
>>
>> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
>
> <snip>
>
>> @@ -11406,7 +11391,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>> vcpu->mode = OUTSIDE_GUEST_MODE;
>> smp_wmb();
>>
>> - kvm_load_host_xfeatures(vcpu);
>> + kvm_load_xfeatures(vcpu, kvm_host.xcr0, kvm_host.xss);
>
> Nit: given that xcr0/xss are either guest or host values, would it be slightly
> better for this helper to accept a boolean (e.g., bool load_guest) to convey
> that the API loads guest (or host) values rather than arbitrary xcr0/xss
> values? like fpu_swap_kvm_fpstate().
This really is a good idea!
Allow arbitrary input but skip the write when vcpu->arch.{xcr0,ia32_xss}
== kvm_host.{xcr0,ia32_xss} does introduce confusion.
> static void kvm_load_xfeatures(struct kvm_vcpu *vcpu, bool load_guest)
> {
> u64 xcr0 = load_guest ? vcpu->arch.xcr0 : kvm_host.xcr0;
> u64 xss = load_guest ? vcpu->arch.ia32_xss : kvm_host.xss;
>
> if (vcpu->arch.guest_state_protected)
> return;
>
>> /*
>> * Sync xfd before calling handle_exit_irqoff() which may
>>
>> base-commit: a996dd2a5e1ec54dcf7d7b93915ea3f97e14e68a
>> prerequisite-patch-id: 9aafd634f0ab2033d7b032e227d356777469e046
>> prerequisite-patch-id: 656ce1f5aa97c77a9cf6125713707a5007b2c7ba
>> prerequisite-patch-id: d6328b8c0fdb8593bb534ab7378821edcf9f639d
>> prerequisite-patch-id: c7f36d1cedc4ae6416223d2225460944629b3d4f
>> --
>> 2.46.0
>>
>>
>
^ permalink raw reply [flat|nested] 5+ messages in thread
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2025-11-06 10:11 [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS Binbin Wu
2025-11-07 3:14 ` Chao Gao
2025-11-07 4:21 ` Binbin Wu
2025-11-07 19:09 ` Sean Christopherson
2025-11-07 6:17 ` Xiaoyao Li
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