On Mon, May 16, 2022, David Matlack wrote:
> The quadrant is only used when gptes are 4 bytes, but
> mmu_alloc_{direct,shadow}_roots() pass in a non-zero quadrant for PAE
> page directories regardless. Make this less confusing by only passing in
> a non-zero quadrant when it is actually necessary.
>
> Signed-off-by: David Matlack <dmatlack@xxxxxxxxxx>
> ---
One nit, otherwise
Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> arch/x86/kvm/mmu/mmu.c | 18 ++++++++++++++----
> 1 file changed, 14 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 515e0b33144a..8508c4bfddb5 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3406,9 +3406,10 @@ static hpa_t mmu_alloc_root(struct kvm_vcpu *vcpu, gfn_t gfn, int quadrant,
> struct kvm_mmu_page *sp;
>
> role.level = level;
> + role.quadrant = quadrant;
>
> - if (role.has_4_byte_gpte)
> - role.quadrant = quadrant;
> + WARN_ON_ONCE(quadrant && !role.has_4_byte_gpte);
> + WARN_ON_ONCE(role.direct && role.has_4_byte_gpte);
>
> sp = kvm_mmu_get_page(vcpu, gfn, role);
> ++sp->root_count;
> @@ -3444,7 +3445,7 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
> for (i = 0; i < 4; ++i) {
> WARN_ON_ONCE(IS_VALID_PAE_ROOT(mmu->pae_root[i]));
>
> - root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT), i,
> + root = mmu_alloc_root(vcpu, i << (30 - PAGE_SHIFT), 0,
> PT32_ROOT_LEVEL);
> mmu->pae_root[i] = root | PT_PRESENT_MASK |
> shadow_me_mask;
> @@ -3529,6 +3530,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> struct kvm_mmu *mmu = vcpu->arch.mmu;
> u64 pdptrs[4], pm_mask;
> gfn_t root_gfn, root_pgd;
> + unsigned int quadrant;
> hpa_t root;
> unsigned i;
Not really your fault, but this manages to use three different type declarations
for quadrant. i is a bare "unsigned", quadrant an "unsigned int" here, and then
@quadrant in mmu_alloc_root() is an "int".
I suspect the "unsigned i" is originated with the "i << (30 - PAGE_SHIFT)" in
mmu_alloc_direct_roots(), though even that can't create a negative value.
Given that quadrant is tiny and "int i" is a de facto standard for iterator values,
my preference would be to opportunisticaly consolidate this to
int quadrant, i, r;
> int r;
> @@ -3614,7 +3616,15 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> root_gfn = pdptrs[i] >> PAGE_SHIFT;
> }
>
> - root = mmu_alloc_root(vcpu, root_gfn, i, PT32_ROOT_LEVEL);
> + /*
> + * If shadowing 32-bit non-PAE page tables, each PAE page
> + * directory maps one quarter of the guest's non-PAE page
> + * directory. Othwerise each PAE page direct shadows one guest
> + * PAE page directory so that quadrant should be 0.
> + */
> + quadrant = (mmu->cpu_role.base.level == PT32_ROOT_LEVEL) ? i : 0;
> +
> + root = mmu_alloc_root(vcpu, root_gfn, quadrant, PT32_ROOT_LEVEL);
> mmu->pae_root[i] = root | pm_mask;
> }
>
> --
> 2.36.0.550.gb090851708-goog
>
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