On 10/28/22 06:52, Mark Brown wrote:

The architecture requires that any system which implements SME also has
fine grained traps since SME is a v9.2 feature, meaning that v8.7 must be
implemented, and FGT is mandatory from v8.6. SME relies on fine grained
traps to control access to SMPRI_EL1 and in nVHE mode to TPIDR2_EL0,
without traps SMPRI_EL1.Priority and TPIDR2_EL0 can be used as side
channels.

This series adds support for detecting FGT and refuses to allow KVM to
be used in architecturally invalid configurations which have SME but not
FGT, without detection the issue presents as faults due to EL2
attempting to access the FGT registers which isn't obvious to users.
Currently fine grained traps are only used in nVHE but but a series
"arm64/sme: Fix SMPRI_EL1 traps for KVM guests" sent along with this
will add usage for VHE mode too making the issue more pressing.

Series:
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~


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