On Tue, Oct 27, 2020 at 2:43 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> Add a helper to compute the GFN mask given a hugepage level, KVM is
> accumulating quite a few users with the addition of the TDP MMU.
>
> Note, gcc is clever enough to use a single NEG instruction instead of
> SUB+NOT, i.e. use the more common "~(level -1)" pattern instead of
> round_gfn_for_level()'s direct two's complement trickery.
As far as I can tell this patch has no functional changes intended.
Please correct me if that's not correct.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/mmu/mmu.c | 2 +-
> arch/x86/kvm/mmu/paging_tmpl.h | 4 ++--
> arch/x86/kvm/mmu/tdp_iter.c | 2 +-
> 4 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d44858b69353..6ea046415f29 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -119,6 +119,7 @@
> #define KVM_HPAGE_SIZE(x) (1UL << KVM_HPAGE_SHIFT(x))
> #define KVM_HPAGE_MASK(x) (~(KVM_HPAGE_SIZE(x) - 1))
> #define KVM_PAGES_PER_HPAGE(x) (KVM_HPAGE_SIZE(x) / PAGE_SIZE)
> +#define KVM_HPAGE_GFN_MASK(x) (~(KVM_PAGES_PER_HPAGE(x) - 1))
NIT: I know x follows the convention on adjacent macros, but this
would be clearer to me if x was changed to level. (Probably for all
the macros in this block)
>
> static inline gfn_t gfn_to_index(gfn_t gfn, gfn_t base_gfn, int level)
> {
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 17587f496ec7..3bfc7ee44e51 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2886,7 +2886,7 @@ static int __direct_map(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> disallowed_hugepage_adjust(*it.sptep, gfn, it.level,
> &pfn, &level);
>
> - base_gfn = gfn & ~(KVM_PAGES_PER_HPAGE(it.level) - 1);
> + base_gfn = gfn & KVM_HPAGE_GFN_MASK(it.level);
> if (it.level == level)
> break;
>
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 50e268eb8e1a..76ee36f2afd2 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -698,7 +698,7 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, gpa_t addr,
> disallowed_hugepage_adjust(*it.sptep, gw->gfn, it.level,
> &pfn, &level);
>
> - base_gfn = gw->gfn & ~(KVM_PAGES_PER_HPAGE(it.level) - 1);
> + base_gfn = gw->gfn & KVM_HPAGE_GFN_MASK(it.level);
> if (it.level == level)
> break;
>
> @@ -751,7 +751,7 @@ FNAME(is_self_change_mapping)(struct kvm_vcpu *vcpu,
> bool *write_fault_to_shadow_pgtable)
> {
> int level;
> - gfn_t mask = ~(KVM_PAGES_PER_HPAGE(walker->level) - 1);
> + gfn_t mask = KVM_HPAGE_GFN_MASK(walker->level);
> bool self_changed = false;
>
> if (!(walker->pte_access & ACC_WRITE_MASK ||
> diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c
> index 87b7e16911db..c6e914c96641 100644
> --- a/arch/x86/kvm/mmu/tdp_iter.c
> +++ b/arch/x86/kvm/mmu/tdp_iter.c
> @@ -17,7 +17,7 @@ static void tdp_iter_refresh_sptep(struct tdp_iter *iter)
>
> static gfn_t round_gfn_for_level(gfn_t gfn, int level)
> {
> - return gfn & -KVM_PAGES_PER_HPAGE(level);
> + return gfn & KVM_HPAGE_GFN_MASK(level);
> }
>
> /*
> --
> 2.28.0
>
