Re: [PATCH v4] KVM: arm64: Record whether pKVM stage 2 mapping is cacheable

On Sun, 05 Jul 2026 15:08:58 +0100,
Dev Jain [off-list ref] wrote:

On 02/07/26 12:54 am, Bradley Morgan wrote:

quoted

pKVM keeps its own mapping list for stage 2 operations. Its flush path
uses that list directly, so it lost the PTE attribute check done by the
generic stage 2 walker.

Record whether a mapping is cacheable and skip cache maintenance for
mappings that are not cacheable.

Fixes: e912efed485a ("KVM: arm64: Introduce the EL1 pKVM MMU")

Is Fixes tag required? If I am reading correctly, Arm ARM says this:

"For VA-based cache maintenance instructions, the instruction operates on the
caches regardless of the memory type and cacheability attributes marked for
the memory address in the VMSA translation table entries. This means that
the effects of the cache maintenance instructions can apply regardless of:
  Whether the address accessed:
    Is Normal memory or Device memory.
    Has the Cacheable attribute or the Non-cacheable attribute."

So nothing goes wrong if we do dcache clean for non-cacheable
memory.

Two things:

- having to perform CMOs for something that is not *expected* to be
  cacheable is both pointless and a contradiction of the intent

- what you quote is about the nature of the *mapping*, and not the
  memory that is being mapped. Cleaning a dirty cache line on an
  unsuspecting MMIO endpoint is never going to end nicely. Just have a
  try.

My reading of all this is that a fix indeed is required, and therefore
a Fixes tag *must* be present.

	M.

-- 
Jazz isn't dead. It just smells funny.