Re: [PATCH] KVM: arm64: Fix the upper limit of the walker range

[Suzuki K Poulose]

On 16/01/2025 10:55, Marc Zyngier wrote:
> On Thu, 16 Jan 2025 01:16:40 +0000,
> Mark Brown <broonie@xxxxxxxxxx> wrote:
> > On Tue, Jan 14, 2025 at 02:50:51PM +0000, Sebastian Ene wrote:
> >
> > > Prevent the walker from running into weeds when walking an
> > > entire address range.
> >
> > The KVM page_fault_test selftest started failing in next-20250115 on
> > at least n1sdp and TX2 in VHE mode and a bisect seems to point to this
> > change.  The bisect only just finished, I've done no further
> > investigation.
> >
> > When the test fails it generates backtraces like that below:
>
> [...]
>
> Thanks for the heads up.
>
> Given how close we are to the merge window opening, I've dropped this
> patch from -next.
>
> Seb: it looks this breaks a bunch of existing assumptions. Let's
> revisit this before -rc1, if possible.
In kvm_pgtable_walk() we set the walk_data.end to PAGE_ALIGNED(start + 
size), where size is BIT(ia_size) and start = 0, for 
kvm_pgtable_stage2_destroy().

And subtracting the limit in _kvm_pgtable_walk makes things go bad,
 returning -ERANGE.
Given the kvm_pgtable_walk() passes the "end" as the top address (not 
including it), and is always PAGE_ALIGNED, we should probably leave 
things as it is in the code.


Cheers
Suzuki


> Thanks,
>
> 	M.