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| author | Sean Christopherson <seanjc@google.com> | 2021-06-22 20:56:55 +0300 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2021-06-25 01:00:37 +0300 |
| commit | 00a669780ffa8c4b5f3e37346b5bf45508dd15bb (patch) | |
| tree | 1ec241e7862ee532db7e6f02c859c1dee65a8664 /Documentation/virt | |
| parent | ddc16abbbae9cd21705323d47158fb9c334438ba (diff) | |
| download | linux-00a669780ffa8c4b5f3e37346b5bf45508dd15bb.tar.xz | |
KVM: x86/mmu: Use MMU role to check for matching guest page sizes
Originally, __kvm_sync_page used to check the cr4_pae bit in the role
to avoid zapping 4-byte kvm_mmu_pages when guest page size are 8-byte
or the other way round. However, in commit 47c42e6b4192 ("KVM: x86: fix
handling of role.cr4_pae and rename it to 'gpte_size'", 2019-03-28) it
was observed that this did not work for nested EPT, where the page table
size would be 8 bytes even if CR4.PAE=0. (Note that the check still
has to be done for nested *NPT*, so it is not possible to use tdp_enabled
or similar).
Therefore, a hack was introduced to identify nested EPT shadow pages
and unconditionally call __kvm_sync_page() on them. However, it is
possible to do without the hack to identify nested EPT shadow pages:
if EPT is active, there will be no shadow pages in non-EPT format,
and all of them will have gpte_is_8_bytes set to true; we can just
check the MMU role directly, and the test will always be true.
Even for non-EPT shadow MMUs, this test should really always be true
now that __kvm_sync_page() is called if and only if the role is an
exact match (kvm_mmu_get_page()) or is part of the current MMU context
(kvm_mmu_sync_roots()). A future commit will convert the likely-pointless
check into a meaningful WARN to enforce that the mmu_roles of the current
context and the shadow page are compatible.
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-11-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/mmu.rst | 3 |
1 files changed, 0 insertions, 3 deletions
diff --git a/Documentation/virt/kvm/mmu.rst b/Documentation/virt/kvm/mmu.rst index 20d85daed395..ddbb23998742 100644 --- a/Documentation/virt/kvm/mmu.rst +++ b/Documentation/virt/kvm/mmu.rst @@ -192,9 +192,6 @@ Shadow pages contain the following information: Contains the value of cr4.smap && !cr0.wp for which the page is valid (pages for which this is true are different from other pages; see the treatment of cr0.wp=0 below). - role.ept_sp: - This is a virtual flag to denote a shadowed nested EPT page. ept_sp - is true if "cr0_wp && smap_andnot_wp", an otherwise invalid combination. role.smm: Is 1 if the page is valid in system management mode. This field determines which of the kvm_memslots array was used to build this |