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SubjectRe: [PATCH 1/2] KVM: x86/mmu: Don't skip non-leaf SPTEs when zapping all SPTEs
Date
On 12/08/21 07:07, Sean Christopherson wrote:
> @@ -739,8 +749,16 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> gfn_t start, gfn_t end, bool can_yield, bool flush,
> bool shared)
> {
> + bool zap_all = (end == ZAP_ALL_END);
> struct tdp_iter iter;
>
> + /*
> + * Bound the walk at host.MAXPHYADDR, guest accesses beyond that will
> + * hit a #PF(RSVD) and never get to an EPT Violation/Misconfig / #NPF,
> + * and so KVM will never install a SPTE for such addresses.
> + */
> + end = min(end, 1ULL << (shadow_phys_bits - PAGE_SHIFT));

Then zap_all need not have any magic value. You can use 0/-1ull, it's
readable enough. ZAP_ALL_END is also unnecessary here if you do:

gfn_t max_gfn_host = 1ULL << (shadow_phys_bits - PAGE_SHIFT);
bool zap_all = (start == 0 && end >= max_gfn_host);

end = min(end, max_gfn_host);

And as a small commit message nit, I would say "don't leak" instead of
"don't skip", since that's really the effect.

Paolo


> kvm_lockdep_assert_mmu_lock_held(kvm, shared);
>
> rcu_read_lock();
> @@ -759,9 +777,10 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root,
> /*
> * If this is a non-last-level SPTE that covers a larger range
> * than should be zapped, continue, and zap the mappings at a
> - * lower level.
> + * lower level, except when zapping all SPTEs.
> */
> - if ((iter.gfn < start ||
> + if (!zap_all &&
> + (iter.gfn < start ||
> iter.gfn + KVM_PAGES_PER_HPAGE(iter.level) > end) &&

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