Re: [PATCH stable-5.8] KVM: arm64: Assume write fault on S1PTW permission fault on instruction fetch

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 29, 2020 at 01:16:34AM +0530, Naresh Kamboju wrote:
> On Mon, 28 Sep 2020 at 23:16, Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > On Mon, Sep 28, 2020 at 06:18:50PM +0100, Marc Zyngier wrote:
> > > Commit c4ad98e4b72cb5be30ea282fce935248f2300e62 upstream.
> > >
> > > KVM currently assumes that an instruction abort can never be a write.
> > > This is in general true, except when the abort is triggered by
> > > a S1PTW on instruction fetch that tries to update the S1 page tables
> > > (to set AF, for example).
> > >
> > > This can happen if the page tables have been paged out and brought
> > > back in without seeing a direct write to them (they are thus marked
> > > read only), and the fault handling code will make the PT executable(!)
> > > instead of writable. The guest gets stuck forever.
> > >
> > > In these conditions, the permission fault must be considered as
> > > a write so that the Stage-1 update can take place. This is essentially
> > > the I-side equivalent of the problem fixed by 60e21a0ef54c ("arm64: KVM:
> > > Take S1 walks into account when determining S2 write faults").
> > >
> > > Update kvm_is_write_fault() to return true on IABT+S1PTW, and introduce
> > > kvm_vcpu_trap_is_exec_fault() that only return true when no faulting
> > > on a S1 fault. Additionally, kvm_vcpu_dabt_iss1tw() is renamed to
> > > kvm_vcpu_abt_iss1tw(), as the above makes it plain that it isn't
> > > specific to data abort.
> > >
> > > Signed-off-by: Marc Zyngier <maz@kernel.org>
> > > Reviewed-by: Will Deacon <will@kernel.org>
> > > Cc: stable@vger.kernel.org
> > > Link: https://lore.kernel.org/r/20200915104218.1284701-2-maz@kernel.org
> >
> > Thanks for all 3 of these, now queued up!
> 
> stable rc branch 4.19 arm64 build broken.
> 
> ../arch/arm64/kvm/../../../virt/kvm/arm/mmu.c:1283:13: error:
> redefinition of ‘kvm_is_write_fault’
>  1283 | static bool kvm_is_write_fault(struct kvm_vcpu *vcpu)
>       |             ^~~~~~~~~~~~~~~~~~
> 
> Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>

Thanks, I'll go drop this patch from the 4.19.y queue and wait for a
fixed up version from Marc.

greg k-h