Re: [PATCH] KVM: SVM: make svm_flush_tlb_gva do a full asid flush if NPT enabled

[Paolo Bonzini]

On 7/27/26 21:58, Yosry Ahmed wrote:
> On Mon, Jul 27, 2026 at 12:23 PM Tycho Andersen <tycho@xxxxxxxxxx> wrote:
> > Hi all,
> >
> > On Thu, Jul 23, 2026 at 11:44:19AM +0200, Paolo Bonzini wrote:
> > > As to the workload, Alexander threw more or less everything at the same
> > > time at the VM:
> > >
> > > - a full Windows Defender scan every 30 minutes
> > >
> > > - a disk I/O job
> > >
> > > - a loop doing repeated mmap of system files (mostly to hope that
> > >    it triggers some consistency check in the Windows memory manager)
> > >
> > > - SQL Express 2022 + StressDB (1.6M rows), with the host doing queries
> > >    (75% write/25% read) via sqlcmd
> >
> > Can you share the code for the mmap + disk io + DB content generator?
> >
> > We're looking at this and would like to reproduce.
>
> Not sure if this is relevant, but I see that hyperv_tlb_flush is flaky
> with npt=0 on Turin at the tip of kvm-x86/next (commit 567329869b9c7).

Same on Milan, but ept=0 works.

> It's not likely because the problem fixed by this patch happens
> specifically with npt=1 and not npt=0 AFAICT, but it is a weird
> coincidence :)

And also because this patch uses, in the end, the same flush mechanism 
that npt=0 and ept=0 already use.  So that bug is probably in npt=0.

That said, I'll do a quick experiment of running hyperv_tlb_flush in a 
loop with this patch.

Paolo

> Maybe something is wrong in the Hyper-V code that manifests
> differently with npt=0/1?