Re: [PATCH 0/4] KVM: arm64: Fix host access to the EL2 stacks

[Marc Zyngier <maz@kernel.org>]

On Tue, 08 Sep 2026 12:07:09 +0100,
Fuad Tabba <fuad.tabba@linux.dev> wrote:
> 
> Hi folks,
> 
> The per-CPU EL2 stacks are initialised as host-owned after pKVM init.
> fix_host_ownership() walks only the linear-map alias of each memblock
> region, and the stacks, mapped in the private VA range for their guard
> pages, have none.
> 
> Patch 1 is the fix, and it needs none of the other three. Patch 4 adds
> the check that would have caught it and would catch similar instances
> in the future: once the transfer is done, walk the private VA range and
> fail init unless every valid leaf is hyp-owned, or is hyp text mapped
> without write access.
> 
> Patch 2 is a fix in its own right, but to a different bug.
> fix_host_ownership_walker() matches hyp text on its stage-1 permissions,
> and that test hasn't matched on a non-hVHE host since 7.0, so hyp text
> is donated there rather than left read-only. Nothing crashes, but the
> instruction dump on hyp panic reads a page the host can't access, so
> the Code: line comes out as question marks. It matches by physical
> address instead, which is what patch 4 needs too. Patch 3 splits the
> start of the range from the allocation cursor, with no functional
> change, so patch 4 knows where the range begins.

Reviewed-by: Marc Zyngier <maz@kernel.org>

	M.

-- 
Without deviation from the norm, progress is not possible.