Messages in this thread | | | Subject | Re: [PATCH] KVM: mmu: Fix SPTE encoding of MMIO generation upper half | From | Paolo Bonzini <> | Date | Sun, 6 Dec 2020 11:09:43 +0100 |
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On 05/12/20 01:48, Maciej S. Szmigiero wrote: > From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com> > > 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> > ---
Good catch. What do you think about this alternative definition? It computes everything from the bit ranges.
#define MMIO_SPTE_GEN_LOW_START 3 #define MMIO_SPTE_GEN_LOW_END 11
#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)
#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)
Thanks,
Paolo
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