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    SubjectRe: Should SEV-ES #VC use IST? (Re: [PATCH] Allow RDTSC and RDTSCP from userspace)
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    On 23/06/2020 13:47, Peter Zijlstra wrote:
    > On Tue, Jun 23, 2020 at 12:51:03PM +0100, Andrew Cooper wrote:
    >
    >> There are cases which are definitely non-recoverable.
    >>
    >> For both ES and SNP, a malicious hypervisor can mess with the guest
    >> physmap to make the the NMI, #VC and #DF stacks all alias.
    >>
    >> For ES, this had better result in the #DF handler deciding that crashing
    >> is the way out, whereas for SNP, this had better escalate to Shutdown.
    >> Crashing out hard if the hypervisor is misbehaving is acceptable.
    > Then I'm thinking the only sensible option is to crash hard for any SNP
    > #VC from kernel mode.
    >
    > Sadly that doesn't help with #VC needing to be IST :-( IST is such a
    > frigging nightmare.

    I presume you mean any #VC caused by RMP faults (i.e. something went
    wrong with the memory owner/etc metadata) ?

    If so, then yes.  Any failure here is a bug in the kernel or hypervisor
    (and needs fixing) or a malicious hypervisor and the guest should
    terminate for its own safety.

    ~Andrew

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