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    SubjectRe: [PATCH v19 046/130] KVM: x86/mmu: Add address conversion functions for TDX shared bit of GPA
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    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
    > + * gfn_to_shared() nop set S bit
    > + * 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.
    > + */
    > +static inline gfn_t kvm_gfn_shared_mask(const struct kvm *kvm)
    > +{
    > + return kvm->arch.gfn_shared_mask;
    > +}
    > +
    > +static inline gfn_t kvm_gfn_to_shared(const struct kvm *kvm, gfn_t gfn)
    > +{
    > + return gfn | kvm_gfn_shared_mask(kvm);
    > +}
    > +
    > +static inline gfn_t kvm_gfn_to_private(const struct kvm *kvm, gfn_t gfn)
    > +{
    > + return gfn & ~kvm_gfn_shared_mask(kvm);
    > +}
    > +
    > +static inline bool kvm_is_private_gpa(const struct kvm *kvm, gpa_t gpa)
    > +{
    > + gfn_t mask = kvm_gfn_shared_mask(kvm);
    > +
    > + return mask && !(gpa_to_gfn(gpa) & mask);
    > +}
    > +
    > #endif
    > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
    > index aa1da51b8af7..54e0d4efa2bd 100644
    > --- a/arch/x86/kvm/vmx/tdx.c
    > +++ b/arch/x86/kvm/vmx/tdx.c
    > @@ -906,6 +906,11 @@ static int tdx_td_init(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
    > kvm_tdx->attributes = td_params->attributes;
    > kvm_tdx->xfam = td_params->xfam;
    >
    > + if (td_params->exec_controls & TDX_EXEC_CONTROL_MAX_GPAW)
    > + kvm->arch.gfn_shared_mask = gpa_to_gfn(BIT_ULL(51));
    > + else
    > + kvm->arch.gfn_shared_mask = gpa_to_gfn(BIT_ULL(47));
    > +
    > out:
    > /* kfree() accepts NULL. */
    > kfree(init_vm);

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