On 2021-04-26 11:36, Marc Zyngier wrote:

Sumit Gupta and Krishna Reddy both reported that for MMIO regions
mapped into userspace using VFIO, a PTE update can trigger a MMU
notifier reaching kvm_set_spte_hva().

There is an assumption baked in kvm_set_spte_hva() that it only
deals with memory pages, and not MMIO. For this purpose, it
performs a cache cleaning of the potentially newly mapped page.
However, for a MMIO range, this explodes as there is no linear
mapping for this range (and doing cache maintenance on it would
make little sense anyway).

Check for the validity of the page before performing the CMO
addresses the problem.

Reported-by: Krishna Reddy <vdumpa@nvidia.com>
Reported-by: Sumit Gupta <sumitg@nvidia.com>,
Tested-by: Sumit Gupta <sumitg@nvidia.com>,
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: 
https://lore.kernel.org/r/5a8825bc-286e-b316-515f-3bd3c9c70a80@nvidia.com (local)

FWIW, I've locally added:

Fixes: 694556d54f35 ("KVM: arm/arm64: Clean dcache to PoC when changing 
PTE due to CoW")
Cc: stable@vger.kernel.org

         M.
-- 
Jazz is not dead. It just smells funny...

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