linux-kernel - Re: [PATCH 05/12] KVM: x86: Use KVM-governed feature framework to track "XSAVES enabled"

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Message-ID: <20230221145610.ytlj5nkqsscc2yxo@linux.intel.com>
Date:   Tue, 21 Feb 2023 22:56:10 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/12] KVM: x86: Use KVM-governed feature framework to
 track "XSAVES enabled"

On Fri, Feb 17, 2023 at 03:10:15PM -0800, Sean Christopherson wrote:
> Use the governed feature framework to track if XSAVES is "enabled", i.e.
> if XSAVES can be used by the guest.  Add a comment in the SVM code to
> explain the very unintuitive logic of deliberately NOT checking if XSAVES
> is enumerated in the guest CPUID model.
> 
> No functional change intended.

xsaves_enabled in struct kvm_vcpu_arch is no longer used. But instead of
just deleting it, maybe we could move 'bool load_eoi_exitmap_pending' to
its place, so 7 bytes can be saved for each struct kvm_vcpu_arch:

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index cd660de02f7b..0eef5469c165 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -740,7 +740,6 @@ struct kvm_vcpu_arch {
        u64 efer;
        u64 apic_base;
        struct kvm_lapic *apic;    /* kernel irqchip context */
-       bool load_eoi_exitmap_pending;
        DECLARE_BITMAP(ioapic_handled_vectors, 256);
        unsigned long apic_attention;
        int32_t apic_arb_prio;
@@ -750,7 +749,7 @@ struct kvm_vcpu_arch {
        u64 smi_count;
        bool at_instruction_boundary;
        bool tpr_access_reporting;
-       bool xsaves_enabled;
+       bool load_eoi_exitmap_pending;
        bool xfd_no_write_intercept;
        u64 ia32_xss;
        u64 microcode_version;

B.R.
Yu