diff options
author | David Matlack <dmatlack@google.com> | 2022-01-13 23:30:19 +0000 |
---|---|---|
committer | Paolo Bonzini <pbonzini@redhat.com> | 2022-01-19 12:07:06 -0500 |
commit | 5f16bcac6e280a7dade580d9627f5cf93ef6aa56 (patch) | |
tree | c681ede4a333e6ec0fb340f1aa170860667702a6 /arch | |
parent | f082d86ea68559e4bd1ecaffa04981b72281e28f (diff) | |
download | linux-5f16bcac6e280a7dade580d9627f5cf93ef6aa56.tar.bz2 |
KVM: x86/mmu: Document and enforce MMU-writable and Host-writable invariants
SPTEs are tagged with software-only bits to indicate if it is
"MMU-writable" and "Host-writable". These bits are used to determine why
KVM has marked an SPTE as read-only.
Document these bits and their invariants, and enforce the invariants
with new WARNs in spte_can_locklessly_be_made_writable() to ensure they
are not accidentally violated in the future.
Opportunistically move DEFAULT_SPTE_{MMU,HOST}_WRITABLE next to
EPT_SPTE_{MMU,HOST}_WRITABLE since the new documentation applies to
both.
No functional change intended.
Signed-off-by: David Matlack <dmatlack@google.com>
Message-Id: <20220113233020.3986005-4-dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/x86/kvm/mmu/spte.h | 42 |
1 files changed, 36 insertions, 6 deletions
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h index a4af2a42695c..be6a007a4af3 100644 --- a/arch/x86/kvm/mmu/spte.h +++ b/arch/x86/kvm/mmu/spte.h @@ -60,10 +60,6 @@ static_assert(SPTE_TDP_AD_ENABLED_MASK == 0); (((address) >> PT64_LEVEL_SHIFT(level)) & ((1 << PT64_LEVEL_BITS) - 1)) #define SHADOW_PT_INDEX(addr, level) PT64_INDEX(addr, level) -/* Bits 9 and 10 are ignored by all non-EPT PTEs. */ -#define DEFAULT_SPTE_HOST_WRITEABLE BIT_ULL(9) -#define DEFAULT_SPTE_MMU_WRITEABLE BIT_ULL(10) - /* * The mask/shift to use for saving the original R/X bits when marking the PTE * as not-present for access tracking purposes. We do not save the W bit as the @@ -79,6 +75,35 @@ static_assert(SPTE_TDP_AD_ENABLED_MASK == 0); static_assert(!(SPTE_TDP_AD_MASK & SHADOW_ACC_TRACK_SAVED_MASK)); /* + * *_SPTE_HOST_WRITEABLE (aka Host-writable) indicates whether the host permits + * writes to the guest page mapped by the SPTE. This bit is cleared on SPTEs + * that map guest pages in read-only memslots and read-only VMAs. + * + * Invariants: + * - If Host-writable is clear, PT_WRITABLE_MASK must be clear. + * + * + * *_SPTE_MMU_WRITEABLE (aka MMU-writable) indicates whether the shadow MMU + * allows writes to the guest page mapped by the SPTE. This bit is cleared when + * the guest page mapped by the SPTE contains a page table that is being + * monitored for shadow paging. In this case the SPTE can only be made writable + * by unsyncing the shadow page under the mmu_lock. + * + * Invariants: + * - If MMU-writable is clear, PT_WRITABLE_MASK must be clear. + * - If MMU-writable is set, Host-writable must be set. + * + * If MMU-writable is set, PT_WRITABLE_MASK is normally set but can be cleared + * to track writes for dirty logging. For such SPTEs, KVM will locklessly set + * PT_WRITABLE_MASK upon the next write from the guest and record the write in + * the dirty log (see fast_page_fault()). + */ + +/* Bits 9 and 10 are ignored by all non-EPT PTEs. */ +#define DEFAULT_SPTE_HOST_WRITEABLE BIT_ULL(9) +#define DEFAULT_SPTE_MMU_WRITEABLE BIT_ULL(10) + +/* * Low ignored bits are at a premium for EPT, use high ignored bits, taking care * to not overlap the A/D type mask or the saved access bits of access-tracked * SPTEs when A/D bits are disabled. @@ -316,8 +341,13 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check, static inline bool spte_can_locklessly_be_made_writable(u64 spte) { - return (spte & shadow_host_writable_mask) && - (spte & shadow_mmu_writable_mask); + if (spte & shadow_mmu_writable_mask) { + WARN_ON_ONCE(!(spte & shadow_host_writable_mask)); + return true; + } + + WARN_ON_ONCE(spte & PT_WRITABLE_MASK); + return false; } static inline u64 get_mmio_spte_generation(u64 spte) |