On Mon, Jun 14, 2021 at 07:07:56PM +0000, Sean Christopherson wrote:
> On Fri, Jun 11, 2021, David Matlack wrote:
> > Refactor is_tdp_mmu_root() into is_vcpu_using_tdp_mmu() to reduce
> > duplicated code at call sites and make the code more readable.
> >
> > Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> > ---
> > arch/x86/kvm/mmu/mmu.c | 10 +++++-----
> > arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
> > arch/x86/kvm/mmu/tdp_mmu.h | 8 +++++---
> > 3 files changed, 11 insertions(+), 9 deletions(-)
> >
>
> ...
I'm not sure how to interpret this.
>
> > diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> > index 5fdf63090451..c8cf12809fcf 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.h
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> > @@ -91,16 +91,18 @@ static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
> > static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
> > #endif
> >
> > -static inline bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
> > +static inline bool is_vcpu_using_tdp_mmu(struct kvm_vcpu *vcpu)
>
> I normally like code reduction, but I think in this case we should stay with
> something closer to the existing code.
>
> If interpreted literally as "is the vCPU using the TDP MMU", the helper is flat
> out broken if arch.mmu points at guest_mmu, in which case the function will
> evaluate "false" even if the _vCPU_ is using the TDP MMU for the non-nested MMU.
Good point. is_vcpu_using_tdp_mmu is ambiguous: It's not clear if it's
checking if the vcpu is using the TDP MMU "right now" versus "at all".
>
> We could dance around that by doing something like:
>
> if (is_current_mmu_tdp_mmu(vcpu))
> ....
>
> but IMO that's a net negative versus:
>
> if (is_tdp_mmu(vcpu, vcpu->arch.mmu))
> ...
>
> because it's specifically the MMU that is of interest.
I agree this is more clear.
>
> > {
> > + struct kvm *kvm = vcpu->kvm;
> > struct kvm_mmu_page *sp;
> > + hpa_t root_hpa = vcpu->arch.mmu->root_hpa;
> >
> > if (!is_tdp_mmu_enabled(kvm))
>
> If we want to eliminate the second param from the prototype, I think we'd be
> better off evaluating whether or not this check buys us anything. Or even better,
> eliminate redundant calls to minimize the benefits so that the "fast" check is
> unnecessary.
>
> The extra check in kvm_tdp_mmu_map() can simply be dropped; it's sole caller
> literally wraps it with a is_tdp_mmu... check.
>
> > return false;
> > - if (WARN_ON(!VALID_PAGE(hpa)))
> > + if (WARN_ON(!VALID_PAGE(root_hpa)))
>
> And hoist this check out of is_tdp_mmu(). I think it's entirely reasonable to
> expect the caller to first test the validity of the root before caring about
> whether it's a TDP MMU or legacy MMU.
>
> The VALID_PAGE() checks here and in__direct_map() and FNAME(page_fault) are also
> mostly worthless, but they're at least a marginally not-awful sanity check and
> not fully redundant.
>
> E.g. achieve this over 2-4 patches:
Thanks for the suggestions, I'll take a look at cleaning that up. I am
thinking of making that a separate patch series (including removing this
patch from this series) as the interaction between the two is entirely
superficial. Let me know if that makes sense.
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index f96fc3cd5c18..527305c8cede 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2899,9 +2899,6 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> gfn_t gfn = gpa >> PAGE_SHIFT;
> gfn_t base_gfn = gfn;
>
> - if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
> - return RET_PF_RETRY;
> -
> level = kvm_mmu_hugepage_adjust(vcpu, gfn, max_level, &pfn,
> huge_page_disallowed, &req_level);
>
> @@ -3635,7 +3632,7 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
> return reserved;
> }
>
> - if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> + if (is_tdp_mmu(vcpu->arch.mmu))
> leaf = kvm_tdp_mmu_get_walk(vcpu, addr, sptes, &root);
> else
> leaf = get_walk(vcpu, addr, sptes, &root);
> @@ -3801,6 +3798,7 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
> static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> bool prefault, int max_level, bool is_tdp)
> {
> + bool is_tdp_mmu_fault = is_tdp_mmu(vcpu->arch.mmu);
> bool write = error_code & PFERR_WRITE_MASK;
> bool map_writable;
>
> @@ -3810,10 +3808,13 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> hva_t hva;
> int r;
>
> + if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
> + return RET_PF_RETRY;
> +
> if (page_fault_handle_page_track(vcpu, error_code, gfn))
> return RET_PF_EMULATE;
>
> - if (!is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)) {
> + if (!is_tdp_mmu_fault) {
> r = fast_page_fault(vcpu, gpa, error_code);
> if (r != RET_PF_INVALID)
> return r;
> @@ -3835,7 +3836,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>
> r = RET_PF_RETRY;
>
> - if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> + if (is_tdp_mmu_fault)
> read_lock(&vcpu->kvm->mmu_lock);
> else
> write_lock(&vcpu->kvm->mmu_lock);
> @@ -3846,7 +3847,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> if (r)
> goto out_unlock;
>
> - if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> + if (is_tdp_mmu_fault)
> r = kvm_tdp_mmu_map(vcpu, gpa, error_code, map_writable, max_level,
> pfn, prefault);
> else
> @@ -3854,7 +3855,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> prefault, is_tdp);
>
> out_unlock:
> - if (is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa))
> + if (is_tdp_mmu_fault)
> read_unlock(&vcpu->kvm->mmu_lock);
> else
> write_unlock(&vcpu->kvm->mmu_lock);
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index cc13e001f3de..7ce90bc50774 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -979,11 +979,6 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> int level;
> int req_level;
>
> - if (WARN_ON(!VALID_PAGE(vcpu->arch.mmu->root_hpa)))
> - return RET_PF_RETRY;
> - if (WARN_ON(!is_tdp_mmu_root(vcpu->kvm, vcpu->arch.mmu->root_hpa)))
> - return RET_PF_RETRY;
> -
> level = kvm_mmu_hugepage_adjust(vcpu, gfn, max_level, &pfn,
> huge_page_disallowed, &req_level);
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index f7a7990da11d..6ebe2331a641 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -92,16 +92,11 @@ static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
> static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
> #endif
>
> -static inline bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
> +static inline bool is_tdp_mmu(struct kvm_mmu *mmu)
> {
> struct kvm_mmu_page *sp;
>
> - if (!is_tdp_mmu_enabled(kvm))
> - return false;
> - if (WARN_ON(!VALID_PAGE(hpa)))
> - return false;
> -
> - sp = to_shadow_page(hpa);
> + sp = to_shadow_page(mmu->root_hpa);
> if (WARN_ON(!sp))
> return false;
>
