On 2/2/26 23:33, Peter Maydell wrote:
In our handling of the boolean 'sme' CPU property, we write this 0/1
value directly to ID_AA64PFR1_EL1.SME. This worked when the only
valid values in that field were 0 (for no SME) and 1 (for SME1).
However, with the addition of SME2 the SME field can now also read 2.
This means that "-cpu max,sme=on" will result in an inconsistent set
of ID registers, where ID_AA64PFR1_EL1.SME claims SME1 but
ID_AA64SMFR0_EL1.SMEver claims SME2p1. This isn't a valid thing to
report, and confuses Linux into reporting SME2 to userspace but not
actually enabling userspace access for it.
Fix this bug by having arm_cpu_sme_finalize() fix up the
ID_AA64PFR1_EL1.SME field to match ID_AA64SMFR0.SMEver. This means
the "sme" property's semantics are "off" for "no SME" and "on" for
"enable at whatever the default SME version this CPU provides is".
Update the documentation to clarify what 'sve=on' and 'sme=on' do.
(We don't have the equivalent bug for 'sve=on' because
ID_AA64PFR0_EL1.SVE only has 0 and 1 as valid values, but the
semantics of the property are the same.)
Cc:[email protected]
Signed-off-by: Peter Maydell<[email protected]>
---
docs/system/arm/cpu-features.rst | 10 ++++++++++
target/arm/cpu64.c | 15 +++++++++++++++
2 files changed, 25 insertions(+)
Reviewed-by: Richard Henderson <[email protected]>
r~
