tree b7cd023c846235d0d45d0e37858ddfbc09e8d94f
parent 3518d60213e8aad2ff346c5c731fd30107410881
author Mark Brown <broonie@kernel.org> 1726141175 +0100
committer Fuad Tabba <tabba@google.com> 1729072036 +0100

KVM: arm64: Constrain the host to the maximum shared SVE VL with pKVM

When pKVM saves and restores the host floating point state on a SVE system
it programs the vector length in ZCR_EL2.LEN to be whatever the maximum VL
for the PE is but uses a buffer allocated with kvm_host_sve_max_vl, the
maximum VL shared by all PEs in the system. This means that if we run on a
system where the maximum VLs are not consistent we will overflow the buffer
on PEs which support larger VLs.

Since the host will not currently attempt to make use of non-shared VLs fix
this by explicitly setting the EL2 VL to be the maximum shared VL when we
save and restore. This will enforce the limit on host VL usage. Should we
wish to support asymmetric VLs this code will need to be updated along with
the required changes for the host, patches have previously been posted:

  https://lore.kernel.org/r/20240730-kvm-arm64-fix-pkvm-sve-vl-v6-0-cae8a2e0bd66@kernel.org

Fixes: b5b9955617bc ("KVM: arm64: Eagerly restore host fpsimd/sve state in pKVM")
Signed-off-by: Mark Brown <broonie@kernel.org>