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    SubjectRe: [PATCH 4.14 038/190] KVM: x86: only do L1TF workaround on affected processors
    On Wed, Jun 24, 2020 at 12:00:59PM +0000, Rantala, Tommi T. (Nokia - FI/Espoo) wrote:
    >On Fri, 2020-06-19 at 16:31 +0200, Greg Kroah-Hartman wrote:
    >> From: Paolo Bonzini <pbonzini@redhat.com>
    >>
    >> [ Upstream commit d43e2675e96fc6ae1a633b6a69d296394448cc32 ]
    >>
    >> KVM stores the gfn in MMIO SPTEs as a caching optimization. These are
    >> split
    >> in two parts, as in "[high 11111 low]", to thwart any attempt to use these
    >> bits
    >> in an L1TF attack. This works as long as there are 5 free bits between
    >> MAXPHYADDR and bit 50 (inclusive), leaving bit 51 free so that the MMIO
    >> access triggers a reserved-bit-set page fault.
    >
    >Hi, I'm now seeing this warning in VM bootup with 4.14.y

    Thanks for the report!

    >Not seen with 4.19.129 and 5.4.47 that also included this commit.
    >
    >Any ideas what's missing in 4.14 ?

    I think that this was because we're missing 6129ed877d40 ("KVM: x86/mmu:
    Set mmio_value to '0' if reserved #PF can't be generated"). I've queued
    it up (along with a few other related commits) and a new -rc cycle
    should be underway for those.

    --
    Thanks,
    Sasha

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