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KVM: x86: fix handling of role.cr4_pae and rename it to 'gpte_size'

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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: 7dcd575520 ("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>
This commit is contained in:
Sean Christopherson
2019-03-07 15:27:44 -08:00
committed by Paolo Bonzini
parent 552c69b1dc
commit 47c42e6b41
4 changed files with 35 additions and 22 deletions
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4
arch/x86/include/asm/kvm_host.h
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@@ -253,14 +253,14 @@ struct kvm_mmu_memory_cache {
* kvm_memory_slot.arch.gfn_track which is 16 bits, so the role bits used
* by indirect shadow page can not be more than 15 bits.
*
* Currently, we used 14 bits that are @level, @cr4_pae, @quadrant, @access,
* Currently, we used 14 bits that are @level, @gpte_is_8_bytes, @quadrant, @access,
* @nxe, @cr0_wp, @smep_andnot_wp and @smap_andnot_wp.
*/
union kvm_mmu_page_role {
u32 word;
struct {
unsigned level:4;
unsigned cr4_pae:1;
unsigned gpte_is_8_bytes:1;
unsigned quadrant:2;
unsigned direct:1;
unsigned access:3;