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    SubjectRe: [PATCH RFC 03/39] KVM: x86/xen: register shared_info page
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    On 12/2/20 5:17 AM, Ankur Arora wrote:
    > On 2020-12-01 5:26 p.m., David Woodhouse wrote
    >> On Tue, 2020-12-01 at 16:40 -0800, Ankur Arora wrote:
    >>> On 2020-12-01 5:07 a.m., David Woodhouse wrote:

    [...]

    >>>> If that was allowed, wouldn't it have been a much simpler fix for
    >>>> CVE-2019-3016? What am I missing?
    >>>
    >>> Agreed.
    >>>
    >>> Perhaps, Paolo can chime in with why KVM never uses pinned page
    >>> and always prefers to do cached mappings instead?
    >>>
    >>>>
    >>>> Should I rework these to use kvm_write_guest_cached()?
    >>>
    >>> kvm_vcpu_map() would be better. The event channel logic does RMW operations
    >>> on shared_info->vcpu_info.
    >>
    >> I've ported the shared_info/vcpu_info parts and made a test case, and
    >> was going back through to make it use kvm_write_guest_cached(). But I
    >> should probably plug on through the evtchn bits before I do that.
    >>
    >> I also don't see much locking on the cache, and can't convince myself
    >> that accessing the shared_info page from multiple CPUs with
    >> kvm_write_guest_cached() or kvm_map_gfn() is sane unless they each have
    >> their own cache.
    >
    > I think you could get a VCPU specific cache with kvm_vcpu_map().
    >

    steal clock handling creates such a mapping cache (struct gfn_to_pfn_cache).

    Joao

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