Re: [RFC PATCH v2 22/25] KVM: x86/mmu: Refactor kvm_mmu_invlpg() to allow skipping the gva flush

[Yosry Ahmed <yosry@kernel.org>]

On Wed, Jul 22, 2026 at 05:56:19PM -0700, Sean Christopherson wrote:
> On Wed, Jul 22, 2026, Sean Christopherson wrote:
> > On Tue, Jun 16, 2026, Yosry Ahmed wrote:
> > > Refactor helpers out of kvm_mmu_invalidate_addr() and kvm_mmu_invlpg()
> > > that take in an extra argument to skip the GVA flush.
> > > 
> > > This will be used when invalidating GVAs in a different context than the
> > > correct one (i.e.  invalidating an L2 GVA from L1), so flushing the
> > > current context would flush the wrong TLB entries.
> > > 
> > > No functional change intended.
> > > 
> > > Signed-off-by: Yosry Ahmed <yosry@kernel.org>
> > > ---
> > >  arch/x86/kvm/mmu/mmu.c | 23 +++++++++++++++++------
> > >  1 file changed, 17 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index 65c35ed8f4a01..3feb75732f7b4 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -6615,15 +6615,15 @@ static void kvm_mmu_invalidate_addr_in_root(struct kvm_vcpu *vcpu,
> > >  	write_unlock(&vcpu->kvm->mmu_lock);
> > >  }
> > >  
> > > -void kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> > > -			     u64 addr, unsigned long roots)
> > > +static void __kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> > > +				      u64 addr, unsigned long roots, bool flush_gva)
> > >  {
> > >  	int i;
> > >  
> > >  	WARN_ON_ONCE(roots & ~KVM_MMU_ROOTS_ALL);
> > >  
> > >  	/* It's actually a GPA for vcpu->arch.guest_mmu.  */
> > > -	if (mmu != &vcpu->arch.guest_mmu) {
> > > +	if (flush_gva && mmu != &vcpu->arch.guest_mmu) {
> > >  		/* INVLPG on a non-canonical address is a NOP according to the SDM.  */
> > >  		if (is_noncanonical_invlpg_address(addr, vcpu))
> > >  			return;
> > > @@ -6642,9 +6642,15 @@ void kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> > >  			kvm_mmu_invalidate_addr_in_root(vcpu, mmu, addr, mmu->prev_roots[i].hpa);
> > >  	}
> > >  }
> > > +
> > > +void kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> > > +			       u64 addr, unsigned long roots)
> > 
> > Rather than kvm_mmu_invalidate_addr() for the wrapper, what if we call this
> > kvm_mmu_invalidate_gva()?  And then kvm_mmu_invlpg_gva().  Then we don't need
> > to have the "in_root" version to a quad-underscores helper, and IMO it's more
> > obvious what's different between the one-line wrappers and the inner helpers.
> 
> Hrm, or maybe I'm not understanding what "flush_gva" means.  At first glance, I
> was assuming you were using it to differentiate between GVA and GPA, but IIUC,
> it's literally skipping the flush for the current context, which just so happens
> to be done only for GVAs.  I'd still like to avoid the "in_root" helper, if at
> all possible.

Yes, it's skipping the TLB flush that is only needed for GVAs. The
alternative I had in mind (but thought was worse) was to refactor the
TLB flush part out of kvm_mmu_invalidate_addr() (or
__kvm_mmu_invalidate_addr()) in this patch instead of adding a boolean,
but this still requires adding a wrapper and the possibility of a
quad-underscore helper.

What's the main objection to kvm_mmu_invalidate_addr_in_root()?