diff options
author | Paolo Bonzini <pbonzini@redhat.com> | 2022-02-09 02:49:47 -0500 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-02-25 08:20:18 -0500 |
commit | 5499ea73e7db5113bb6f60c9122495ddcd900940 (patch) | |
tree | b4e4a39bc8932aea6293f82e2700c6bd5dfd80ab /arch/x86/kvm/mmu/mmu.c | |
parent | 0c1c92f15f7600a03377e3211983f3571c08ad4b (diff) |
KVM: x86/mmu: look for a cached PGD when going from 32-bit to 64-bit
Right now, PGD caching avoids placing a PAE root in the cache by using the
old value of mmu->root_level and mmu->shadow_root_level; it does not look
for a cached PGD if the old root is a PAE one, and then frees it using
kvm_mmu_free_roots.
Change the logic instead to free the uncacheable root early.
This way, __kvm_new_mmu_pgd is able to look up the cache when going from
32-bit to 64-bit (if there is a hit, the invalid root becomes the least
recently used). An example of this is nested virtualization with shadow
paging, when a 64-bit L1 runs a 32-bit L2.
As a side effect (which is actually the reason why this patch was
written), PGD caching does not use the old value of mmu->root_level
and mmu->shadow_root_level anymore.
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch/x86/kvm/mmu/mmu.c')
-rw-r--r-- | arch/x86/kvm/mmu/mmu.c | 82 |
1 files changed, 59 insertions, 23 deletions
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 07cc9b155e6d..9783d74b3f95 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4085,52 +4085,88 @@ static inline bool is_root_usable(struct kvm_mmu_root_info *root, gpa_t pgd, union kvm_mmu_page_role role) { return (role.direct || pgd == root->pgd) && - VALID_PAGE(root->hpa) && to_shadow_page(root->hpa) && + VALID_PAGE(root->hpa) && role.word == to_shadow_page(root->hpa)->role.word; } /* - * Find out if a previously cached root matching the new pgd/role is available. - * The current root is also inserted into the cache. - * If a matching root was found, it is assigned to kvm_mmu->root.hpa and true is - * returned. - * Otherwise, the LRU root from the cache is assigned to kvm_mmu->root.hpa and - * false is returned. This root should now be freed by the caller. + * Find out if a previously cached root matching the new pgd/role is available, + * and insert the current root as the MRU in the cache. + * If a matching root is found, it is assigned to kvm_mmu->root and + * true is returned. + * If no match is found, kvm_mmu->root is left invalid, the LRU root is + * evicted to make room for the current root, and false is returned. */ -static bool cached_root_available(struct kvm_vcpu *vcpu, gpa_t new_pgd, - union kvm_mmu_page_role new_role) +static bool cached_root_find_and_keep_current(struct kvm *kvm, struct kvm_mmu *mmu, + gpa_t new_pgd, + union kvm_mmu_page_role new_role) { uint i; - struct kvm_mmu *mmu = vcpu->arch.mmu; if (is_root_usable(&mmu->root, new_pgd, new_role)) return true; for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) { + /* + * The swaps end up rotating the cache like this: + * C 0 1 2 3 (on entry to the function) + * 0 C 1 2 3 + * 1 C 0 2 3 + * 2 C 0 1 3 + * 3 C 0 1 2 (on exit from the loop) + */ swap(mmu->root, mmu->prev_roots[i]); - if (is_root_usable(&mmu->root, new_pgd, new_role)) - break; + return true; } - return i < KVM_MMU_NUM_PREV_ROOTS; + kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT); + return false; } -static bool fast_pgd_switch(struct kvm_vcpu *vcpu, gpa_t new_pgd, - union kvm_mmu_page_role new_role) +/* + * Find out if a previously cached root matching the new pgd/role is available. + * On entry, mmu->root is invalid. + * If a matching root is found, it is assigned to kvm_mmu->root, the LRU entry + * of the cache becomes invalid, and true is returned. + * If no match is found, kvm_mmu->root is left invalid and false is returned. + */ +static bool cached_root_find_without_current(struct kvm *kvm, struct kvm_mmu *mmu, + gpa_t new_pgd, + union kvm_mmu_page_role new_role) { - struct kvm_mmu *mmu = vcpu->arch.mmu; + uint i; + + for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) + if (is_root_usable(&mmu->prev_roots[i], new_pgd, new_role)) + goto hit; + return false; + +hit: + swap(mmu->root, mmu->prev_roots[i]); + /* Bubble up the remaining roots. */ + for (; i < KVM_MMU_NUM_PREV_ROOTS - 1; i++) + mmu->prev_roots[i] = mmu->prev_roots[i + 1]; + mmu->prev_roots[i].hpa = INVALID_PAGE; + return true; +} + +static bool fast_pgd_switch(struct kvm *kvm, struct kvm_mmu *mmu, + gpa_t new_pgd, union kvm_mmu_page_role new_role) +{ /* - * For now, limit the fast switch to 64-bit hosts+VMs in order to avoid + * For now, limit the caching to 64-bit hosts+VMs in order to avoid * having to deal with PDPTEs. We may add support for 32-bit hosts/VMs * later if necessary. */ - if (mmu->shadow_root_level >= PT64_ROOT_4LEVEL && - mmu->root_level >= PT64_ROOT_4LEVEL) - return cached_root_available(vcpu, new_pgd, new_role); + if (VALID_PAGE(mmu->root.hpa) && !to_shadow_page(mmu->root.hpa)) + kvm_mmu_free_roots(kvm, mmu, KVM_MMU_ROOT_CURRENT); - return false; + if (VALID_PAGE(mmu->root.hpa)) + return cached_root_find_and_keep_current(kvm, mmu, new_pgd, new_role); + else + return cached_root_find_without_current(kvm, mmu, new_pgd, new_role); } static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd, @@ -4138,8 +4174,8 @@ static void __kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd, { struct kvm_mmu *mmu = vcpu->arch.mmu; - if (!fast_pgd_switch(vcpu, new_pgd, new_role)) { - kvm_mmu_free_roots(vcpu->kvm, mmu, KVM_MMU_ROOT_CURRENT); + if (!fast_pgd_switch(vcpu->kvm, mmu, new_pgd, new_role)) { + /* kvm_mmu_ensure_valid_pgd will set up a new root. */ return; } |