Re: [PATCH v19 046/130] KVM: x86/mmu: Add address conversion functions for TDX shared bit of GPA

Isaku Yamahata
2024-03-27T23:50:55Z

On Wed, Mar 27, 2024 at 10:09:21PM +0800,
Binbin Wu <binbin.wu@linux.intel.com> wrote:

>
>
> On 3/27/2024 11:08 AM, Chenyi Qiang wrote:
> >
> > On 2/26/2024 4:25 PM, isaku.yamahata@intel.com wrote:
> > > From: Isaku Yamahata <isaku.yamahata@intel.com>
> > >
> > > TDX repurposes one GPA bit (51 bit or 47 bit based on configuration) to
> > > indicate the GPA is private(if cleared) or shared (if set) with VMM. If
> > > GPA.shared is set, GPA is covered by the existing conventional EPT pointed
> > > by EPTP. If GPA.shared bit is cleared, GPA is covered by TDX module.
> > > VMM has to issue SEAMCALLs to operate.
> > >
> > > Add a member to remember GPA shared bit for each guest TDs, add address
> > > conversion functions between private GPA and shared GPA and test if GPA
> > > is private.
> > >
> > > Because struct kvm_arch (or struct kvm which includes struct kvm_arch. See
> > > kvm_arch_alloc_vm() that passes __GPF_ZERO) is zero-cleared when allocated,
> > > the new member to remember GPA shared bit is guaranteed to be zero with
> > > this patch unless it's initialized explicitly.
> > >
> > > default or SEV-SNP TDX: S = (47 or 51) - 12
> > > gfn_shared_mask 0 S bit
> > > kvm_is_private_gpa() always false true if GFN has S bit set
> > TDX: true if GFN has S bit clear?
> >
> > > kvm_gfn_to_shared() nop set S bit
> > > kvm_gfn_to_private() nop clear S bit
> > >
> > > fault.is_private means that host page should be gotten from guest_memfd
> > > is_private_gpa() means that KVM MMU should invoke private MMU hooks.
> > >
> > > Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> > > Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> > > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > > Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
> > > ---
> > > v19:
> > > - Add comment on default vm case.
> > > - Added behavior table in the commit message
> > > - drop CONFIG_KVM_MMU_PRIVATE
> > >
> > > v18:
> > > - Added Reviewed-by Binbin
> > >
> > > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> > > ---
> > > arch/x86/include/asm/kvm_host.h | 2 ++
> > > arch/x86/kvm/mmu.h | 33 +++++++++++++++++++++++++++++++++
> > > arch/x86/kvm/vmx/tdx.c | 5 +++++
> > > 3 files changed, 40 insertions(+)
> > >
> > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > > index 5da3c211955d..de6dd42d226f 100644
> > > --- a/arch/x86/include/asm/kvm_host.h
> > > +++ b/arch/x86/include/asm/kvm_host.h
> > > @@ -1505,6 +1505,8 @@ struct kvm_arch {
> > > */
> > > #define SPLIT_DESC_CACHE_MIN_NR_OBJECTS (SPTE_ENT_PER_PAGE + 1)
> > > struct kvm_mmu_memory_cache split_desc_cache;
> > > +
> > > + gfn_t gfn_shared_mask;
> > > };
> > > struct kvm_vm_stat {
> > > diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> > > index d96c93a25b3b..395b55684cb9 100644
> > > --- a/arch/x86/kvm/mmu.h
> > > +++ b/arch/x86/kvm/mmu.h
> > > @@ -322,4 +322,37 @@ static inline gpa_t kvm_translate_gpa(struct kvm_vcpu *vcpu,
> > > return gpa;
> > > return translate_nested_gpa(vcpu, gpa, access, exception);
> > > }
> > > +
> > > +/*
> > > + * default or SEV-SNP TDX: where S = (47 or 51) - 12
> > > + * gfn_shared_mask 0 S bit
> > > + * is_private_gpa() always false if GPA has S bit set
>
> Also here,
> TDX: true if GFN has S bit cleared

Oops. Will fix both.
--
Isaku Yamahata <isaku.yamahata@intel.com>