Hi Peter,
On 11/6/25 11:31, Peter Maydell wrote:
On Wed, 5 Nov 2025 at 17:49, Gustavo Romero <[email protected]> wrote:
Hi Gabriel,
Thanks for your contribution.
On 11/4/25 21:50, Gabriel Brookman wrote:
FEAT_MTE_TAGGED_FAR is a feature required for MTE4. The feature
guarantees that the full address (including tag bits) is reported after
a SEGV_MTESERR, and advertises itself in the ID_AA64PFR2_EL1 system
register. QEMU was already reporting the full address, so this commit
simply advertises the feature by setting that register, and unsets the
register if MTE is disabled.
Signed-off-by: Gabriel Brookman <[email protected]>
---
This patch is the first step toward implementing ARM's Enhanced Memory
Tagging Extension (MTE4). MTE4 guarantees the presence of several
subfeatures: FEAT_MTE_CANONICAL_TAGS, FEAT_MTE_TAGGED_FAR,
FEAT_MTE_STORE_ONLY, FEAT_MTE_NO_ADDRESS_TAGS, and FEAT_MTE_PERM,
none of which are currently implemented in QEMU.
According to the ARM ARM, the presence of any of these features (except
FEAT_MTE_PERM) implies the presence of all the others. For simplicity
and ease of review, I plan to introduce them one at a time. This first
patch focuses on FEAT_MTE_TAGGED_FAR.
I think it's ok to add these "subfeatures" separately.
We can add the implementation of the subfeatures separately,
but we should not enable them in 'max' until they're all
present.
ah, true. I forget that when we do that we enable them in 'max'
as a last step.
(We don't always adhere strictly to the architecture's
"feature X implies Y exists" rules,
Thanks for confirming it ;)
but in this case
because they're really a tightly linked bundle that add
up to "MTE4" I think that presnting only a subset to guests
is likely to result in them not behaving correctly.)
Gabriel, given what Peter explained above, although the patch
is correct, the best to move forward here is to embedded this
patch into the additional series that implements the others
"subfeatures" and, as a last step, after the patches that
implement the features, you enable all the features in 'max'.
Cheers,
Gustavo
