Re: [PATCH 1/5] KVM: SVM: Decrypt SEV VMSA in dump_vmcb() if debugging is enabled

[Sean Christopherson]

On Mon, Mar 24, 2025, Tom Lendacky wrote:
> On 3/20/25 08:26, Tom Lendacky wrote:
> > An SEV-ES/SEV-SNP VM save area (VMSA) can be decrypted if the guest
> > policy allows debugging. Update the dump_vmcb() routine to output
> > some of the SEV VMSA contents if possible. This can be useful for
> > debug purposes.
> > 
> > Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> > ---
> >  arch/x86/kvm/svm/sev.c | 98 ++++++++++++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/svm/svm.c | 13 ++++++
> >  arch/x86/kvm/svm/svm.h | 11 +++++
> >  3 files changed, 122 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > index 661108d65ee7..6e3f5042d9ce 100644
> > --- a/arch/x86/kvm/svm/sev.c
> > +++ b/arch/x86/kvm/svm/sev.c
> 
> > +
> > +	if (sev_snp_guest(vcpu->kvm)) {
> > +		struct sev_data_snp_dbg dbg = {0};
> > +
> > +		vmsa = snp_alloc_firmware_page(__GFP_ZERO);
> > +		if (!vmsa)
> > +			return NULL;
> > +
> > +		dbg.gctx_paddr = __psp_pa(sev->snp_context);
> > +		dbg.src_addr = svm->vmcb->control.vmsa_pa;
> > +		dbg.dst_addr = __psp_pa(vmsa);
> > +
> > +		ret = sev_issue_cmd(vcpu->kvm, SEV_CMD_SNP_DBG_DECRYPT, &dbg, &error);
> 
> This can also be sev_do_cmd() where the file descriptor isn't checked.
> Since it isn't really a user initiated call, that might be desirable since
> this could also be useful for debugging during guest destruction (when the
> file descriptor has already been closed) for VMSAs that haven't exited
> with an INVALID exit code.
> 
> Just an FYI, I can change this call and the one below to sev_do_cmd() if
> agreed upon.

Works for me.  Want to provide a delta patch?  I can fixup when applying.