path: root/Documentation
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authorSean Christopherson <sean.j.christopherson@intel.com>2019-03-07 15:27:44 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2019-03-28 17:27:03 +0100
commit47c42e6b4192a2ac8b6c9858ebcf400a9eff7a10 (patch)
tree31f0183b70b90c02ee2aae85558b257110e82f2b /Documentation
parent552c69b1dc714854a5f4e27d37a43c6d797adf7d (diff)
KVM: x86: fix handling of role.cr4_pae and rename it to 'gpte_size'
The cr4_pae flag is a bit of a misnomer, its purpose is really to track whether the guest PTE that is being shadowed is a 4-byte entry or an 8-byte entry. Prior to supporting nested EPT, the size of the gpte was reflected purely by CR4.PAE. KVM fudged things a bit for direct sptes, but it was mostly harmless since the size of the gpte never mattered. Now that a spte may be tracking an indirect EPT entry, relying on CR4.PAE is wrong and ill-named. For direct shadow pages, force the gpte_size to '1' as they are always 8-byte entries; EPT entries can only be 8-bytes and KVM always uses 8-byte entries for NPT and its identity map (when running with EPT but not unrestricted guest). Likewise, nested EPT entries are always 8-bytes. Nested EPT presents a unique scenario as the size of the entries are not dictated by CR4.PAE, but neither is the shadow page a direct map. To handle this scenario, set cr0_wp=1 and smap_andnot_wp=1, an otherwise impossible combination, to denote a nested EPT shadow page. Use the information to avoid incorrectly zapping an unsync'd indirect page in __kvm_sync_page(). Providing a consistent and accurate gpte_size fixes a bug reported by Vitaly where fast_cr3_switch() always fails when switching from L2 to L1 as kvm_mmu_get_page() would force role.cr4_pae=0 for direct pages, whereas kvm_calc_mmu_role_common() would set it according to CR4.PAE. Fixes: 7dcd575520082 ("x86/kvm/mmu: check if tdp/shadow MMU reconfiguration is needed") Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com> Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation')
1 files changed, 7 insertions, 4 deletions
diff --git a/Documentation/virtual/kvm/mmu.txt b/Documentation/virtual/kvm/mmu.txt
index f365102c80f5..2efe0efc516e 100644
--- a/Documentation/virtual/kvm/mmu.txt
+++ b/Documentation/virtual/kvm/mmu.txt
@@ -142,7 +142,7 @@ Shadow pages contain the following information:
If clear, this page corresponds to a guest page table denoted by the gfn
- When role.cr4_pae=0, the guest uses 32-bit gptes while the host uses 64-bit
+ When role.gpte_is_8_bytes=0, the guest uses 32-bit gptes while the host uses 64-bit
sptes. That means a guest page table contains more ptes than the host,
so multiple shadow pages are needed to shadow one guest page.
For first-level shadow pages, role.quadrant can be 0 or 1 and denotes the
@@ -158,9 +158,9 @@ Shadow pages contain the following information:
The page is invalid and should not be used. It is a root page that is
currently pinned (by a cpu hardware register pointing to it); once it is
unpinned it will be destroyed.
- role.cr4_pae:
- Contains the value of cr4.pae for which the page is valid (e.g. whether
- 32-bit or 64-bit gptes are in use).
+ role.gpte_is_8_bytes:
+ Reflects the size of the guest PTE for which the page is valid, i.e. '1'
+ if 64-bit gptes are in use, '0' if 32-bit gptes are in use.
Contains the value of efer.nxe for which the page is valid.
@@ -173,6 +173,9 @@ 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.
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