linux-kernel - Re: [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0 and XSS

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Message-ID: <aQ1kG5u8GPdEwoEy@intel.com>
Date: Fri, 7 Nov 2025 11:14:35 +0800
From: Chao Gao <chao.gao@...el.com>
To: Binbin Wu <binbin.wu@...ux.intel.com>
CC: <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KVM: x86: Add a help to dedup loading guest/host XCR0
 and XSS

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@...ux.intel.com>

Reviewed-by: Chao Gao <chao.gao@...el.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
>
>