Re: [PATCH v5 8/8] selftests: KVM: x86: Add SEV PML dirty logging test

["Huang, Kai" <kai.huang@intel.com>]

On Wed, 2026-01-14 at 19:57 +0530, Nikunj A. Dadhania wrote:
> 
> On 1/14/2026 5:06 PM, Huang, Kai wrote:
> > On Mon, 2026-01-05 at 06:36 +0000, Nikunj A Dadhania wrote:
> > > Add a KVM selftest to verify Page Modification Logging (PML) functionality
> > > with AMD SEV/SEV-ES/SEV-SNP guests. The test validates that
> > > hardware-assisted dirty page tracking works correctly across different SEV
> > > guest types.
> > 
> > Hi Nikunj,
> > 
> > Perhaps a dumb question -- Why do we need specific selftest case for SEV*
> > guests?
> 
> As there was a request from you to check if SEV supports PML,
> I wrote this test and thought to send it as part of this series.

Oh for that I just meant whether PML works for SEV* on hardware level, but
not asking any selftests to confirm.  Sorry about the confusion :-(

I had this question because TDX guests don't support PML, and we needed to
only set kvm->arch.cpu_dirty_log_size for VMX guests. 

Since your patch (IIRC) always sets cpu_dirty_log_size for all AMD VMs (in
svm_init_vm()):

+	if (pml)
+		kvm->arch.cpu_dirty_log_size = PML_LOG_NR_ENTRIES;
+

I thought it would be better to check whether SEV* guests work with PML
"on hardware level", otherwise we need TDX-similar treatment on AMD side,
i.e., to clear cpu_dirty_log_size for SEV* guests.

> 
> > In terms of GPA logging, my understanding is there's no difference between
> > normal AMD SVM guests and SEV* guests from hardware's point of view.  So
> > if PML works for normal AMD SVM guests, it should work for SEV* guests,
> > no?
> 
> Yes, that is correct.
> 
> > 
> > FWIW, a more reasonable selftest case is we probably need a AMD version of
> > vmx_dirty_log_test.c[*], which verifies PML is indeed not enabled when L2
> > runs.
> 
> Yosry has added the support here [1].

Thanks for the info.

Then I don't think we need this new selftest case specifically for SEV*
(assuming [1] will be merged, if it has not been done already).

Again, sorry for the confusion.