The patch below does not apply to the 5.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 34c0f6f2695a2db81e09a3ab7bdb2853f45d4d3d Mon Sep 17 00:00:00 2001

From: "Maciej S. Szmigiero" maciej.szmigiero@oracle.com Date: Sat, 5 Dec 2020 01:48:08 +0100 Subject: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half

Commit cae7ed3c2cb0 ("KVM: x86: Refactor the MMIO SPTE generation handling") cleaned up the computation of MMIO generation SPTE masks, however it introduced a bug how the upper part was encoded: SPTE bits 52-61 were supposed to contain bits 10-19 of the current generation number, however a missing shift encoded bits 1-10 there instead (mostly duplicating the lower part of the encoded generation number that then consisted of bits 1-9).

In the meantime, the upper part was shrunk by one bit and moved by subsequent commits to become an upper half of the encoded generation number (bits 9-17 of bits 0-17 encoded in a SPTE).

In addition to the above, commit 56871d444bc4 ("KVM: x86: fix overlap between SPTE_MMIO_MASK and generation") has changed the SPTE bit range assigned to encode the generation number and the total number of bits encoded but did not update them in the comment attached to their defines, nor in the KVM MMU doc. Let's do it here, too, since it is too trivial thing to warrant a separate commit.

Fixes: cae7ed3c2cb0 ("KVM: x86: Refactor the MMIO SPTE generation handling") Signed-off-by: Maciej S. Szmigiero maciej.szmigiero@oracle.com Message-Id: 156700708db2a5296c5ed7a8b9ac71f1e9765c85.1607129096.git.maciej.szmigiero@oracle.com Cc: stable@vger.kernel.org [Reorganize macros so that everything is computed from the bit ranges. - Paolo] Signed-off-by: Paolo Bonzini pbonzini@redhat.com

diff --git a/Documentation/virt/kvm/mmu.rst b/Documentation/virt/kvm/mmu.rst index 1c030dbac7c4..5bfe28b0728e 100644 --- a/Documentation/virt/kvm/mmu.rst +++ b/Documentation/virt/kvm/mmu.rst @@ -455,7 +455,7 @@ If the generation number of the spte does not equal the global generation number, it will ignore the cached MMIO information and handle the page fault through the slow path.

-Since only 19 bits are used to store generation-number on mmio spte, all +Since only 18 bits are used to store generation-number on mmio spte, all pages are zapped when there is an overflow.

Unfortunately, a single memory access might access kvm_memslots(kvm) multiple diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c index fcac2cac78fe..c51ad544f25b 100644 --- a/arch/x86/kvm/mmu/spte.c +++ b/arch/x86/kvm/mmu/spte.c @@ -40,8 +40,8 @@ static u64 generation_mmio_spte_mask(u64 gen) WARN_ON(gen & ~MMIO_SPTE_GEN_MASK); BUILD_BUG_ON((MMIO_SPTE_GEN_HIGH_MASK | MMIO_SPTE_GEN_LOW_MASK) & SPTE_SPECIAL_MASK);

- mask = (gen << MMIO_SPTE_GEN_LOW_START) & MMIO_SPTE_GEN_LOW_MASK; - mask |= (gen << MMIO_SPTE_GEN_HIGH_START) & MMIO_SPTE_GEN_HIGH_MASK; + mask = (gen << MMIO_SPTE_GEN_LOW_SHIFT) & MMIO_SPTE_GEN_LOW_MASK; + mask |= (gen << MMIO_SPTE_GEN_HIGH_SHIFT) & MMIO_SPTE_GEN_HIGH_MASK; return mask; }

diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h index 5c75a451c000..2b3a30bd38b0 100644 --- a/arch/x86/kvm/mmu/spte.h +++ b/arch/x86/kvm/mmu/spte.h @@ -56,11 +56,11 @@ #define SPTE_MMU_WRITEABLE (1ULL << (PT_FIRST_AVAIL_BITS_SHIFT + 1))

/* - * Due to limited space in PTEs, the MMIO generation is a 19 bit subset of + * Due to limited space in PTEs, the MMIO generation is a 18 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 9-18 of the MMIO generation are propagated to spte bits 52-61 + * Bits 9-17 of the MMIO generation are propagated to spte bits 54-62 * * 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 @@ -69,18 +69,29 @@ * requires a full MMU zap). The flag is instead explicitly queried when * checking for MMIO spte cache hits. */ -#define MMIO_SPTE_GEN_MASK GENMASK_ULL(17, 0)

#define MMIO_SPTE_GEN_LOW_START 3 #define MMIO_SPTE_GEN_LOW_END 11 -#define MMIO_SPTE_GEN_LOW_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_END, \ - MMIO_SPTE_GEN_LOW_START)

#define MMIO_SPTE_GEN_HIGH_START PT64_SECOND_AVAIL_BITS_SHIFT #define MMIO_SPTE_GEN_HIGH_END 62 + +#define MMIO_SPTE_GEN_LOW_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_END, \ + MMIO_SPTE_GEN_LOW_START) #define MMIO_SPTE_GEN_HIGH_MASK GENMASK_ULL(MMIO_SPTE_GEN_HIGH_END, \ MMIO_SPTE_GEN_HIGH_START)

+#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 == 9); + +#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) + +#define MMIO_SPTE_GEN_MASK GENMASK_ULL(MMIO_SPTE_GEN_LOW_BITS + MMIO_SPTE_GEN_HIGH_BITS - 1, 0) + extern u64 __read_mostly shadow_nx_mask; extern u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */ extern u64 __read_mostly shadow_user_mask; @@ -228,8 +239,8 @@ static inline u64 get_mmio_spte_generation(u64 spte) { u64 gen;

- gen = (spte & MMIO_SPTE_GEN_LOW_MASK) >> MMIO_SPTE_GEN_LOW_START; - gen |= (spte & MMIO_SPTE_GEN_HIGH_MASK) >> MMIO_SPTE_GEN_HIGH_START; + gen = (spte & MMIO_SPTE_GEN_LOW_MASK) >> MMIO_SPTE_GEN_LOW_SHIFT; + gen |= (spte & MMIO_SPTE_GEN_HIGH_MASK) >> MMIO_SPTE_GEN_HIGH_SHIFT; return gen; }