From: Tom Lendacky <thomas.lendacky@amd.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: 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
Subject: Re: [PATCH 2/2] KVM: x86/mmu: Exclude the MMU_PRESENT bit from MMIO SPTE's generation
Date: Tue, 9 Mar 2021 10:39:46 -0600 [thread overview]
Message-ID: <d7708644-f35a-952a-a0aa-ea376ac6490a@amd.com> (raw)
In-Reply-To: <20210309021900.1001843-3-seanjc@google.com>
On 3/8/21 8:19 PM, Sean Christopherson wrote:
> Drop bit 11, used for the MMU_PRESENT flag, from the set of bits used to
> store the generation number in MMIO SPTEs. MMIO SPTEs with bit 11 set,
> which occurs when userspace creates 128+ memslots in an address space,
> get false positives for is_shadow_present_spte(), which lead to a variety
> of fireworks, crashes KVM, and likely hangs the host kernel.
>
> Fixes: b14e28f37e9b ("KVM: x86/mmu: Use a dedicated bit to track shadow/MMU-present SPTEs")
> Reported-by: Tom Lendacky <thomas.lendacky@amd.com>
Fixes the issue for me. Thanks, Sean.
Tested-by: Tom Lendacky <thomas.lendacky@amd.com>
> Reported-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> arch/x86/kvm/mmu/spte.h | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index b53036d9ddf3..bca0ba11cccf 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -101,11 +101,11 @@ static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK));
> #undef SHADOW_ACC_TRACK_SAVED_MASK
>
> /*
> - * Due to limited space in PTEs, the MMIO generation is a 20 bit subset of
> + * Due to limited space in PTEs, the MMIO generation is a 19 bit subset of
> * the memslots generation and is derived as follows:
> *
> - * Bits 0-8 of the MMIO generation are propagated to spte bits 3-11
> - * Bits 9-19 of the MMIO generation are propagated to spte bits 52-62
> + * Bits 0-7 of the MMIO generation are propagated to spte bits 3-10
> + * Bits 8-18 of the MMIO generation are propagated to spte bits 52-62
> *
> * The KVM_MEMSLOT_GEN_UPDATE_IN_PROGRESS flag is intentionally not included in
> * the MMIO generation number, as doing so would require stealing a bit from
> @@ -116,7 +116,7 @@ static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK));
> */
>
> #define MMIO_SPTE_GEN_LOW_START 3
> -#define MMIO_SPTE_GEN_LOW_END 11
> +#define MMIO_SPTE_GEN_LOW_END 10
>
> #define MMIO_SPTE_GEN_HIGH_START 52
> #define MMIO_SPTE_GEN_HIGH_END 62
> @@ -125,12 +125,14 @@ static_assert(!(EPT_SPTE_MMU_WRITABLE & SHADOW_ACC_TRACK_SAVED_MASK));
> MMIO_SPTE_GEN_LOW_START)
> #define MMIO_SPTE_GEN_HIGH_MASK GENMASK_ULL(MMIO_SPTE_GEN_HIGH_END, \
> MMIO_SPTE_GEN_HIGH_START)
> +static_assert(!(SPTE_MMU_PRESENT_MASK &
> + (MMIO_SPTE_GEN_LOW_MASK | MMIO_SPTE_GEN_HIGH_MASK)));
>
> #define MMIO_SPTE_GEN_LOW_BITS (MMIO_SPTE_GEN_LOW_END - MMIO_SPTE_GEN_LOW_START + 1)
> #define MMIO_SPTE_GEN_HIGH_BITS (MMIO_SPTE_GEN_HIGH_END - MMIO_SPTE_GEN_HIGH_START + 1)
>
> /* remember to adjust the comment above as well if you change these */
> -static_assert(MMIO_SPTE_GEN_LOW_BITS == 9 && MMIO_SPTE_GEN_HIGH_BITS == 11);
> +static_assert(MMIO_SPTE_GEN_LOW_BITS == 8 && MMIO_SPTE_GEN_HIGH_BITS == 11);
>
> #define MMIO_SPTE_GEN_LOW_SHIFT (MMIO_SPTE_GEN_LOW_START - 0)
> #define MMIO_SPTE_GEN_HIGH_SHIFT (MMIO_SPTE_GEN_HIGH_START - MMIO_SPTE_GEN_LOW_BITS)
>
prev parent reply other threads:[~2021-03-09 16:40 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-09 2:18 [PATCH 0/2] Fixups to hide our goofs Sean Christopherson
2021-03-09 2:18 ` [PATCH 1/2] KVM: x86: Fixup "Get active PCID only when writing a CR3 value" Sean Christopherson
2021-03-09 17:26 ` Sean Christopherson
2021-03-09 2:19 ` [PATCH 2/2] KVM: x86/mmu: Exclude the MMU_PRESENT bit from MMIO SPTE's generation Sean Christopherson
2021-03-09 10:09 ` Maxim Levitsky
2021-03-09 13:12 ` Paolo Bonzini
2021-03-09 13:31 ` Maxim Levitsky
2021-03-09 16:39 ` Tom Lendacky [this message]
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