Re: [PATCH Part2 v6 41/49] KVM: SVM: Add support to handle the RMP nested page fault

Jarkko Sakkinen
2022-07-12T12:48:38Z

On Tue, Jul 12, 2022 at 03:45:13PM +0300, Jarkko Sakkinen wrote:
> On Tue, Jul 12, 2022 at 03:34:00PM +0300, Jarkko Sakkinen wrote:
> > On Mon, Jun 20, 2022 at 11:13:03PM +0000, Ashish Kalra wrote:
> > > From: Brijesh Singh <brijesh.singh@amd.com>
> > >
> > > When SEV-SNP is enabled in the guest, the hardware places restrictions on
> > > all memory accesses based on the contents of the RMP table. When hardware
> > > encounters RMP check failure caused by the guest memory access it raises
> > > the #NPF. The error code contains additional information on the access
> > > type. See the APM volume 2 for additional information.
> > >
> > > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> > > ---
> > > arch/x86/kvm/svm/sev.c | 76 ++++++++++++++++++++++++++++++++++++++++++
> > > arch/x86/kvm/svm/svm.c | 14 +++++---
> > > 2 files changed, 86 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > > index 4ed90331bca0..7fc0fad87054 100644
> > > --- a/arch/x86/kvm/svm/sev.c
> > > +++ b/arch/x86/kvm/svm/sev.c
> > > @@ -4009,3 +4009,79 @@ void sev_post_unmap_gfn(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn)
> > >
> > > spin_unlock(&sev->psc_lock);
> > > }
> > > +
> > > +void handle_rmp_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u64 error_code)
> > > +{
> > > + int rmp_level, npt_level, rc, assigned;
> > > + struct kvm *kvm = vcpu->kvm;
> > > + gfn_t gfn = gpa_to_gfn(gpa);
> > > + bool need_psc = false;
> > > + enum psc_op psc_op;
> > > + kvm_pfn_t pfn;
> > > + bool private;
> > > +
> > > + write_lock(&kvm->mmu_lock);
> > > +
> > > + if (unlikely(!kvm_mmu_get_tdp_walk(vcpu, gpa, &pfn, &npt_level)))
> >
> > This function does not exist. Should it be kvm_mmu_get_tdp_page?
>
> Ugh, ignore that.
>
> This the actual issue:
>
> $ git grep kvm_mmu_get_tdp_walk
> arch/x86/kvm/mmu/mmu.c:bool kvm_mmu_get_tdp_walk(struct kvm_vcpu *vcpu, gpa_t gpa, kvm_pfn_t *pfn, int *level)
> arch/x86/kvm/mmu/mmu.c:EXPORT_SYMBOL_GPL(kvm_mmu_get_tdp_walk);
> arch/x86/kvm/svm/sev.c: rc = kvm_mmu_get_tdp_walk(vcpu, gpa, &pfn, &npt_level);
>
> It's not declared in any header.

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 0e1f4d92b89b..33267f619e61 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -164,6 +164,8 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu)
kvm_pfn_t kvm_mmu_map_tdp_page(struct kvm_vcpu *vcpu, gpa_t gpa,
u32 error_code, int max_level);

+bool kvm_mmu_get_tdp_walk(struct kvm_vcpu *vcpu, gpa_t gpa, kvm_pfn_t *pfn, int *level):
+
/*
* Check if a given access (described through the I/D, W/R and U/S bits of a
* page fault error code pfec) causes a permission fault with the given PTE

BTW, kvm_mmu_map_tdp_page() ought to be in single line since it's less than
100 characters.

BR, Jarkko