Re: [Xen-devel] [PATCH V6] x86/hvm: fix domain crash when CR3 has the noflush bit set

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 28.02.18 at 11:38, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> In hardware, when PCID support is enabled and the NOFLUSH bit is set
> when writing a CR3 value, the hardware will clear that that bit and
> change the CR3 without flushing the TLB. hvm_set_cr3(), however, was
> ignoring this bit; the result was that post-vm_event checks detected
> an invalid CR3 value and crashed the domain.
> 
> Handle NOFLUSH in hvm_set_cr3() by:
> 1. Clearing the bit
> 2. Passing a "noflush" flag to lower-level cr3 setting functions to
> indicate that a flush should not be performed.
> 
> Also clear X86_CR3_NOFLUSH when reporting CR3 monitored CR3 writes.
> 
> This allows introspection to be used on VMs whose operating system uses
> the NOFLUSH bit.
> 
> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> Reported-by: Bitweasil <bitweasil@xxxxxxxxxxxxxx>
> Suggested-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Acked-by: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>

There's now the question of whether to backport this change:
It's quite large, and as per the description it deals with an
introspection issue only. Hence for the moment I'll leave this
out. If someone comes forward with good reasons to take this
for some or all of the still maintained older trees, I'm willing to
reconsider. But of course possible interdependencies with
other changes that weren't backported will also need to be
taken into consideration with any such request.

Jan


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