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SubjectRe: [PATCH] KVM: SVM: Issue WBINVD after deactivating an SEV guest
On 3/21/20 4:00 AM, Greg KH wrote:
> On Fri, Mar 20, 2020 at 03:37:23PM -0500, Tom Lendacky wrote:
>> On 3/20/20 3:34 PM, David Rientjes wrote:
>>> On Fri, 20 Mar 2020, Tom Lendacky wrote:
>>>> Currently, CLFLUSH is used to flush SEV guest memory before the guest is
>>>> terminated (or a memory hotplug region is removed). However, CLFLUSH is
>>>> not enough to ensure that SEV guest tagged data is flushed from the cache.
>>>> With 33af3a7ef9e6 ("KVM: SVM: Reduce WBINVD/DF_FLUSH invocations"), the
>>>> original WBINVD was removed. This then exposed crashes at random times
>>>> because of a cache flush race with a page that had both a hypervisor and
>>>> a guest tag in the cache.
>>>> Restore the WBINVD when destroying an SEV guest and add a WBINVD to the
>>>> svm_unregister_enc_region() function to ensure hotplug memory is flushed
>>>> when removed. The DF_FLUSH can still be avoided at this point.
>>>> Fixes: 33af3a7ef9e6 ("KVM: SVM: Reduce WBINVD/DF_FLUSH invocations")
>>>> Signed-off-by: Tom Lendacky <>
>>> Acked-by: David Rientjes <>
>>> Should this be marked for stable?
>> The Fixes tag should take care of that.
> No it does not.
> Please read:
> for how to do this properly.
> Yes, I have had to go around and clean up after maintainers who don't
> seem to realize this, but for KVM patches I have been explicitly told to
> NOT take any patch unless it has a cc: stable on it, due to issues that
> have happened in the past.
> So for this subsystem, what you suggested guaranteed it would NOT get
> picked up, please do not do that.

Thanks for clarifying that, Greg.

Then, yes, it should have the Cc: to stable that David mentioned. If it
gets applied without that, I'll follow the process to send an email to
stable to get it included in 5.5-stable.


> greg k-h

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