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

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Date:   Tue, 12 Jul 2022 15:48:31 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Ashish Kalra <Ashish.Kalra@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        jroedel@...e.de, thomas.lendacky@....com, hpa@...or.com,
        ardb@...nel.org, pbonzini@...hat.com, seanjc@...gle.com,
        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, michael.roth@....com, vbabka@...e.cz,
        kirill@...temov.name, ak@...ux.intel.com, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
        alpergun@...gle.com, dgilbert@...hat.com
Subject: Re: [PATCH Part2 v6 41/49] KVM: SVM: Add support to handle the RMP
 nested page fault

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@....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@....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