On 7/23/22 03:23, Sean Christopherson wrote:
Tag shadow pages that cannot be replaced with an NX huge page even if
zapping the page would not allow KVM to create a huge page, e.g. because
something else prevents creating a huge page. This will allow a future
patch to more precisely apply the mitigation by checking if an existing
shadow page can be replaced by a NX huge page. Currently, KVM assumes
that any existing shadow page encountered cannot be replaced by a NX huge
page (if the mitigation is enabled), which prevents KVM from replacing
no-longer-necessary shadow pages with huge pages, e.g. after disabling
dirty logging, zapping from the mmu_notifier due to page migration,
etc...
Failure to tag shadow pages appropriately could theoretically lead to
false negatives, e.g. if a fetch fault requests a small page and thus
isn't tracked, and a read/write fault later requests a huge page, KVM
will not reject the huge page as it should.
To avoid yet another flag, initialize the list_head and use list_empty()
to determine whether or not a page is on the list of NX huge pages that
should be recovered.
Opportunstically rename most of the variables/functions involved to
provide consistency, e.g. lpage vs huge page and NX huge vs huge NX, and
clarity, e.g. to make it obvious the flag applies only to the NX huge
page mitigation, not to any condition that prevents creating a huge page.
Please do this in a separate patch, since this one is already complex
enough.
* The following two entries are used to key the shadow page in the
@@ -100,7 +106,14 @@ struct kvm_mmu_page {
};
};
- struct list_head lpage_disallowed_link;
+ /*
+ * Use to track shadow pages that, if zapped, would allow KVM to create
s/Use/Used/
Thanks,
Paolo
