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Message-ID: <aAdpp_xAuKMLR0vx@Asmaa.>
Date: Tue, 22 Apr 2025 03:04:23 -0700
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Maxim Levitsky <mlevitsk@...hat.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Jim Mattson <jmattson@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Rik van Riel <riel@...riel.com>,
Tom Lendacky <thomas.lendacky@....com>, x86@...nel.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 13/24] KVM: nSVM: Parameterize svm_flush_tlb_asid()
by is_guest_mode
On Thu, Apr 03, 2025 at 04:10:06PM -0400, Maxim Levitsky wrote:
> On Wed, 2025-03-26 at 19:36 +0000, Yosry Ahmed wrote:
> > svm_flush_tlb_asid() currently operates on the current VMCB. In
> > preparation for properly tracking TLB flushes for L1 and L2 ASIDs,
> > refactor it to take is_guest_mode and find the proper VMCB. All existing
> > callers pass is_guest_mode(vcpu) to maintain existing behavior for now.
> >
> > Move the comment about only flushing the current ASID to
> > svm_flush_tlb_all(), where it probably should have been anyway, because
> > svm_flush_tlb_asid() now flushes a given ASID, not the current ASID.
> >
> > Create a svm_flush_tlb_guest() wrapper to use as the flush_tlb_guest()
> > callback.
> >
> > No functional change intended.
> >
> > Signed-off-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
> > ---
> > arch/x86/kvm/svm/svm.c | 39 +++++++++++++++++++++++++--------------
> > 1 file changed, 25 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> > index 865c5ce4fa473..fb6b9f88a1504 100644
> > --- a/arch/x86/kvm/svm/svm.c
> > +++ b/arch/x86/kvm/svm/svm.c
> > @@ -4016,25 +4016,24 @@ static void svm_enable_nmi_window(struct kvm_vcpu *vcpu)
> > svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);
> > }
> >
> > -static void svm_flush_tlb_asid(struct kvm_vcpu *vcpu)
> > +static struct vmcb *svm_get_vmcb(struct vcpu_svm *svm, bool is_guest_mode)
> > +{
> > + return is_guest_mode ? svm->nested.vmcb02.ptr : svm->vmcb01.ptr;
> > +}
>
> Not sure 100% about this helper, it name might be a bit confusing because
> we already have a current vmcb. Maybe add a comment above stating this
> this is to get vmcb which might not be currently active?
Yeah I spent some time trying to come up with an elaborate name then
convinced myself that the is_guest_mode parameter will make it clear
that the caller specifies which VMCB it wants, regardless of which VMCB
is current.
I can add a comment to make it clearer.
>
> > +
> > +static void svm_flush_tlb_asid(struct kvm_vcpu *vcpu, bool is_guest_mode)
> > {
> > struct vcpu_svm *svm = to_svm(vcpu);
> > + struct vmcb *vmcb = svm_get_vmcb(svm, is_guest_mode);
> >
> > /*
> > * Unlike VMX, SVM doesn't provide a way to flush only NPT TLB entries.
> > * A TLB flush for the current ASID flushes both "host" and "guest" TLB
> > * entries, and thus is a superset of Hyper-V's fine grained flushing.
> > */
> > - kvm_hv_vcpu_purge_flush_tlb(vcpu, is_guest_mode(vcpu));
> > -
> > - /*
> > - * Flush only the current ASID even if the TLB flush was invoked via
> > - * kvm_flush_remote_tlbs(). Although flushing remote TLBs requires all
> > - * ASIDs to be flushed, KVM uses a single ASID for L1 and L2, and
> > - * unconditionally does a TLB flush on both nested VM-Enter and nested
> > - * VM-Exit (via kvm_mmu_reset_context()).
> > - */
> > - vmcb_set_flush_asid(svm->vmcb);
> > + kvm_hv_vcpu_purge_flush_tlb(vcpu, is_guest_mode);
> > + if (vmcb)
> > + vmcb_set_flush_asid(vmcb);
> > }
> >
> > static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
> > @@ -4050,7 +4049,7 @@ static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
> > if (svm_hv_is_enlightened_tlb_enabled(vcpu) && VALID_PAGE(root_tdp))
> > hyperv_flush_guest_mapping(root_tdp);
> >
> > - svm_flush_tlb_asid(vcpu);
> > + svm_flush_tlb_asid(vcpu, is_guest_mode(vcpu));
> > }
> >
> > static void svm_flush_tlb_all(struct kvm_vcpu *vcpu)
> > @@ -4065,7 +4064,14 @@ static void svm_flush_tlb_all(struct kvm_vcpu *vcpu)
> > if (WARN_ON_ONCE(svm_hv_is_enlightened_tlb_enabled(vcpu)))
> > hv_flush_remote_tlbs(vcpu->kvm);
> >
> > - svm_flush_tlb_asid(vcpu);
> > + /*
> > + * Flush only the current ASID even if the TLB flush was invoked via
> > + * kvm_flush_remote_tlbs(). Although flushing remote TLBs requires all
> > + * ASIDs to be flushed, KVM uses a single ASID for L1 and L2, and
> > + * unconditionally does a TLB flush on both nested VM-Enter and nested
> > + * VM-Exit (via kvm_mmu_reset_context()).
> > + */
> > + svm_flush_tlb_asid(vcpu, is_guest_mode(vcpu));
> > }
> >
> > static void svm_flush_tlb_gva(struct kvm_vcpu *vcpu, gva_t gva)
> > @@ -4075,6 +4081,11 @@ static void svm_flush_tlb_gva(struct kvm_vcpu *vcpu, gva_t gva)
> > invlpga(gva, svm_get_current_asid(svm));
> > }
> >
> > +static void svm_flush_tlb_guest(struct kvm_vcpu *vcpu)
> > +{
> > + svm_flush_tlb_asid(vcpu, is_guest_mode(vcpu));
> > +}
> > +
> > static inline void sync_cr8_to_lapic(struct kvm_vcpu *vcpu)
> > {
> > struct vcpu_svm *svm = to_svm(vcpu);
> > @@ -5187,7 +5198,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> > .flush_tlb_all = svm_flush_tlb_all,
> > .flush_tlb_current = svm_flush_tlb_current,
> > .flush_tlb_gva = svm_flush_tlb_gva,
> > - .flush_tlb_guest = svm_flush_tlb_asid,
> > + .flush_tlb_guest = svm_flush_tlb_guest,
> >
> > .vcpu_pre_run = svm_vcpu_pre_run,
> > .vcpu_run = svm_vcpu_run,
>
>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
Thanks!
>
>
> Best regards,
> Maxim Levitsky
>
>
>
>
>
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