Re: [V1 PATCH 1/6] KVM: x86: Add support for testing private memory

[Chao Peng <chao.p.peng@linux.intel.com>]

On Tue, Nov 22, 2022 at 08:06:01PM +0000, Sean Christopherson wrote:
> On Tue, Nov 22, 2022, Chao Peng wrote:
> > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > > index 10017a9f26ee..b3118d00b284 100644
> > > --- a/arch/x86/kvm/mmu/mmu.c
> > > +++ b/arch/x86/kvm/mmu/mmu.c
> > > @@ -4280,6 +4280,10 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> > >  
> > >  	fault->gfn = fault->addr >> PAGE_SHIFT;
> > >  	fault->slot = kvm_vcpu_gfn_to_memslot(vcpu, fault->gfn);
> > > +#ifdef CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING
> > > +	fault->is_private = kvm_slot_can_be_private(fault->slot) &&
> > > +			kvm_mem_is_private(vcpu->kvm, fault->gfn);
> > > +#endif
> > >  
> > >  	if (page_fault_handle_page_track(vcpu, fault))
> > >  		return RET_PF_EMULATE;
> > > diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> > > index 5cdff5ca546c..2e759f39c2c5 100644
> > > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > > @@ -188,7 +188,6 @@ struct kvm_page_fault {
> > >  
> > >  	/* Derived from mmu and global state.  */
> > >  	const bool is_tdp;
> > > -	const bool is_private;
> > >  	const bool nx_huge_page_workaround_enabled;
> > >  
> > >  	/*
> > > @@ -221,6 +220,9 @@ struct kvm_page_fault {
> > >  	/* The memslot containing gfn. May be NULL. */
> > >  	struct kvm_memory_slot *slot;
> > >  
> > > +	/* Derived from encryption bits of the faulting GPA for CVMs. */
> > > +	bool is_private;
> > 
> > Either we can wrap it with the CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING or if
> > it looks ugly I can remove the "const" in my code.
> 
> Hmm, I think we can keep the const.  Similar to the bug in kvm_faultin_pfn()[*],
> the kvm_slot_can_be_private() is bogus.  A fault should be considered private if
> it's marked as private, whether or not userspace has configured the slot to be
> private is irrelevant.  I.e. the xarray is the single source of truth, memslots
> are just plumbing.

That makes sense to me. Thanks.

> 
> Then kvm_mmu_do_page_fault() can do something like:
> 
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index dbaf6755c5a7..456a9daa36e5 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -260,6 +260,8 @@ enum {
>  static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>                                         u32 err, bool prefetch)
>  {
> +       bool is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault);
> +
>         struct kvm_page_fault fault = {
>                 .addr = cr2_or_gpa,
>                 .error_code = err,
> @@ -269,13 +271,15 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>                 .rsvd = err & PFERR_RSVD_MASK,
>                 .user = err & PFERR_USER_MASK,
>                 .prefetch = prefetch,
> -               .is_tdp = likely(vcpu->arch.mmu->page_fault == kvm_tdp_page_fault),
> +               .is_tdp = is_tdp,
>                 .nx_huge_page_workaround_enabled =
>                         is_nx_huge_page_enabled(vcpu->kvm),
>  
>                 .max_level = KVM_MAX_HUGEPAGE_LEVEL,
>                 .req_level = PG_LEVEL_4K,
>                 .goal_level = PG_LEVEL_4K,
> +               .private = IS_ENABLED(CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING) && is_tdp &&
> +                          kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT),
>         };
>         int r;
> 
> [*] https://lore.kernel.org/all/Y3Vgc5KrNRA8r6vh@google.com