linux-kernel - Re: [PATCH v11 09/35] KVM: x86: Determine shared/private faults based on vm

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Date: Mon, 12 Feb 2024 08:27:21 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Michael Roth <michael.roth@....com>, kvm@...r.kernel.org, linux-coco@...ts.linux.dev, 
	linux-mm@...ck.org, linux-crypto@...r.kernel.org, x86@...nel.org, 
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com, 
	jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com, ardb@...nel.org, 
	vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org, 
	dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com, 
	peterz@...radead.org, srinivas.pandruvada@...ux.intel.com, 
	rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de, 
	vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com, 
	sathyanarayanan.kuppuswamy@...ux.intel.com, alpergun@...gle.com, 
	jarkko@...nel.org, ashish.kalra@....com, nikunj.dadhania@....com, 
	pankaj.gupta@....com, liam.merwick@...cle.com, zhi.a.wang@...el.com
Subject: Re: [PATCH v11 09/35] KVM: x86: Determine shared/private faults based
 on vm_type

On Mon, Feb 12, 2024, Paolo Bonzini wrote:
> On Sat, Dec 30, 2023 at 6:24 PM Michael Roth <michael.roth@....com> wrote:
> >
> > For KVM_X86_SNP_VM, only the PFERR_GUEST_ENC_MASK flag is needed to
> > determine with an #NPF is due to a private/shared access by the guest.
> > Implement that handling here. Also add handling needed to deal with
> > SNP guests which in some cases will make MMIO accesses with the
> > encryption bit.
> >
> > Signed-off-by: Michael Roth <michael.roth@....com>
> > ---
> >  arch/x86/kvm/mmu/mmu.c          | 12 ++++++++++--
> >  arch/x86/kvm/mmu/mmu_internal.h | 20 +++++++++++++++++++-
> >  2 files changed, 29 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index d3fbfe0686a0..61213f6648a1 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -4331,6 +4331,7 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> >  static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> >  {
> >         struct kvm_memory_slot *slot = fault->slot;
> > +       bool private_fault = fault->is_private;
> 
> I think it's nicer to just make the fault !is_private in
> kvm_mmu_do_page_fault().

Yeah.  I'm starting to recall more of this discussion.  This is one of the reasons
I suggested/requested stuffing the error code to piggy-back the new SNP bit; doing
so allows is_private to be computed from the get-go without needing any vendor
specific hooks.