From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Ben Gardon <bgardon@google.com>
Subject: [PATCH 23/24] KVM: x86/mmu: Use low available bits for removed SPTEs
Date: Thu, 25 Feb 2021 12:47:48 -0800 [thread overview]
Message-ID: <20210225204749.1512652-24-seanjc@google.com> (raw)
In-Reply-To: <20210225204749.1512652-1-seanjc@google.com>
Use low "available" bits to tag REMOVED SPTEs. Using a high bit is
moderately costly as it often causes the compiler to generate a 64-bit
immediate. More importantly, this makes it very clear REMOVED_SPTE is
a value, not a flag.
Cc: Ben Gardon <bgardon@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/mmu/spte.c | 11 ++++++++++-
arch/x86/kvm/mmu/spte.h | 11 +++++++----
2 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index e07aabb23b8a..66d43cec0c31 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -277,7 +277,16 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask)
SHADOW_NONPRESENT_OR_RSVD_MASK_LEN)))
mmio_value = 0;
- WARN_ON((mmio_value & mmio_mask) != mmio_value);
+ /*
+ * The masked MMIO value must obviously match itself and a removed SPTE
+ * must not get a false positive. Removed SPTEs and MMIO SPTEs should
+ * never collide as MMIO must set some RWX bits, and removed SPTEs must
+ * not set any RWX bits.
+ */
+ if (WARN_ON((mmio_value & mmio_mask) != mmio_value) ||
+ WARN_ON(mmio_value && (REMOVED_SPTE & mmio_mask) == mmio_value))
+ mmio_value = 0;
+
shadow_mmio_value = mmio_value;
shadow_mmio_mask = mmio_mask;
shadow_mmio_access_mask = access_mask;
diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
index 2fad4ccd3679..b53036d9ddf3 100644
--- a/arch/x86/kvm/mmu/spte.h
+++ b/arch/x86/kvm/mmu/spte.h
@@ -174,13 +174,16 @@ extern u64 __read_mostly shadow_nonpresent_or_rsvd_mask;
* non-present intermediate value. Other threads which encounter this value
* should not modify the SPTE.
*
- * This constant works because it is considered non-present on both AMD and
- * Intel CPUs and does not create a L1TF vulnerability because the pfn section
- * is zeroed out.
+ * Use a semi-arbitrary value that doesn't set RWX bits, i.e. is not-present on
+ * bot AMD and Intel CPUs, and doesn't set PFN bits, i.e. doesn't create a L1TF
+ * vulnerability. Use only low bits to avoid 64-bit immediates.
*
* Only used by the TDP MMU.
*/
-#define REMOVED_SPTE (1ull << 59)
+#define REMOVED_SPTE 0x5a0ULL
+
+/* Removed SPTEs must not be misconstrued as shadow present PTEs. */
+static_assert(!(REMOVED_SPTE & SPTE_MMU_PRESENT_MASK));
static inline bool is_removed_spte(u64 spte)
{
--
2.30.1.766.gb4fecdf3b7-goog
next prev parent reply other threads:[~2021-02-25 21:03 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 20:47 [PATCH 00/24] KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs Sean Christopherson
2021-02-25 20:47 ` [PATCH 01/24] KVM: x86/mmu: Set SPTE_AD_WRPROT_ONLY_MASK if and only if PML is enabled Sean Christopherson
2021-02-25 20:47 ` [PATCH 02/24] KVM: x86/mmu: Check for shadow-present SPTE before querying A/D status Sean Christopherson
2021-02-25 20:47 ` [PATCH 03/24] KVM: x86/mmu: Bail from fast_page_fault() if SPTE is not shadow-present Sean Christopherson
2021-02-25 20:47 ` [PATCH 04/24] KVM: x86/mmu: Disable MMIO caching if MMIO value collides with L1TF Sean Christopherson
2021-02-25 20:47 ` [PATCH 05/24] KVM: x86/mmu: Retry page faults that hit an invalid memslot Sean Christopherson
2021-02-25 20:47 ` [PATCH 06/24] KVM: x86/mmu: Don't install bogus MMIO SPTEs if MMIO caching is disabled Sean Christopherson
2021-02-25 20:47 ` [PATCH 07/24] KVM: x86/mmu: Handle MMIO SPTEs directly in mmu_set_spte() Sean Christopherson
2021-02-25 20:47 ` [PATCH 08/24] KVM: x86/mmu: Drop redundant trace_kvm_mmu_set_spte() in the TDP MMU Sean Christopherson
2021-02-25 20:47 ` [PATCH 09/24] KVM: x86/mmu: Rename 'mask' to 'spte' in MMIO SPTE helpers Sean Christopherson
2021-02-25 20:47 ` [PATCH 10/24] KVM: x86/mmu: Stop using software available bits to denote MMIO SPTEs Sean Christopherson
2021-02-25 20:47 ` [PATCH 11/24] KVM: x86/mmu: Add module param to disable MMIO caching (for testing) Sean Christopherson
2021-02-25 20:47 ` [PATCH 12/24] KVM: x86/mmu: Rename and document A/D scheme for TDP SPTEs Sean Christopherson
2021-02-25 20:47 ` [PATCH 13/24] KVM: x86/mmu: Use MMIO SPTE bits 53 and 52 for the MMIO generation Sean Christopherson
2021-02-25 20:47 ` [PATCH 14/24] KVM: x86/mmu: Document dependency bewteen TDP A/D type and saved bits Sean Christopherson
2021-02-25 20:47 ` [PATCH 15/24] KVM: x86/mmu: Move initial kvm_mmu_set_mask_ptes() call into MMU proper Sean Christopherson
2021-02-25 20:47 ` [PATCH 16/24] KVM: x86/mmu: Co-locate code for setting various SPTE masks Sean Christopherson
2021-02-25 20:47 ` [PATCH 17/24] KVM: x86/mmu: Move logic for setting SPTE masks for EPT into the MMU proper Sean Christopherson
2021-02-25 20:47 ` [PATCH 18/24] KVM: x86/mmu: Make Host-writable and MMU-writable bit locations dynamic Sean Christopherson
2021-02-25 20:47 ` [PATCH 19/24] KVM: x86/mmu: Use high bits for host/mmu writable masks for EPT SPTEs Sean Christopherson
2021-02-25 20:47 ` [PATCH 20/24] KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs Sean Christopherson
2021-03-08 18:52 ` Tom Lendacky
2021-03-08 19:48 ` Paolo Bonzini
2021-03-08 20:11 ` Sean Christopherson
2021-03-08 21:49 ` Sean Christopherson
2021-02-25 20:47 ` [PATCH 21/24] KVM: x86/mmu: Tweak auditing WARN for A/D bits to !PRESENT (was MMIO) Sean Christopherson
2021-05-06 23:05 ` Matteo Croce
2021-05-07 7:38 ` Paolo Bonzini
2021-02-25 20:47 ` [PATCH 22/24] KVM: x86/mmu: Use is_removed_spte() instead of open coded equivalents Sean Christopherson
2021-02-25 20:47 ` Sean Christopherson [this message]
2021-02-25 20:47 ` [PATCH 24/24] KVM: x86/mmu: Dump reserved bits if they're detected on non-MMIO SPTE Sean Christopherson
2021-02-26 9:38 ` [PATCH 00/24] KVM: x86/mmu: Introduce MMU_PRESENT and fix bugs Paolo Bonzini
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