Re: [Xen-devel] [PATCH v3] x86/EPT: work around hardware erratum setting A bit

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Oct 02, 2015 at 11:29:54AM +0100, Andrew Cooper wrote:
> On 30/09/15 12:47, Andrew Cooper wrote:
> > On 30/09/15 12:36, Jan Beulich wrote:
> >> Since commit 191b3f3344ee ("p2m/ept: enable PML in p2m-ept for
> >> log-dirty"), the A and D bits of EPT paging entries are set
> >> unconditionally, regardless of whether PML is enabled or not. This
> >> causes a regression in Xen 4.6 on some processors due to Intel Errata
> >> AVR41 -- HVM guests get severe memory corruption when the A bit is set
> >> due to incorrect TLB flushing on mov to cr3. The errata affects the Atom
> >> C2000 family (Avoton).
> >>
> >> To fix, do not set the A bit on this processor family.
> >>
> >> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
> >>
> >> Move feature suppression to feature detection code. Add command line
> >> override.
> >>
> >> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> >>
> >> --- a/docs/misc/xen-command-line.markdown
> >> +++ b/docs/misc/xen-command-line.markdown
> >> @@ -705,19 +705,28 @@ virtualization, to allow the L1 hypervis
> >>  does not provide VM\_ENTRY\_LOAD\_GUEST\_PAT.
> >>  
> >>  ### ept (Intel)
> >> -> `= List of ( pml<boolean> )`
> >> +> `= List of ( pml | ad )`
> > Please keep the type annotations.  Future sub-options might not be
> > boolean parameters.
> >
> > Otherwise, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> >
> > The setup of vmx features looks ripe for some future cleanup, allowing
> > quite a few bits of data to move from __read_mostly into __initdata. 
> > However, the patch does match the prevailing style so should be fixed in
> > this way, given the proximity to the 4.6 release.
> 
> I can no longer reproduce the issue, given this patch.
> 
> Tested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Great! Thanks for testing.

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