diff options
| author | Fuad Tabba <tabba@google.com> | 2024-04-23 16:05:28 +0100 |
|---|---|---|
| committer | Marc Zyngier <maz@kernel.org> | 2024-05-01 16:48:14 +0100 |
| commit | eef4ce6363626cbaabceef64d0bda84c3df922ac (patch) | |
| tree | 7f868edc1ae039df25f29d0fe54b5f6bac9aff88 /arch/arm64/kvm | |
| parent | b6ed4fa9411f7c17ebc69949c1df66dc12b2f827 (diff) | |
KVM: arm64: Clarify rationale for ZCR_EL1 value restored on guest exit
Expand comment clarifying why the host value representing SVE
vector length being restored for ZCR_EL1 on guest exit isn't the
same as it was on guest entry.
Signed-off-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240423150538.2103045-21-tabba@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
Diffstat (limited to 'arch/arm64/kvm')
| -rw-r--r-- | arch/arm64/kvm/fpsimd.c | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 63a6f82934a6..1807d3a79a8a 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -175,12 +175,34 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) if (vcpu_has_sve(vcpu)) { __vcpu_sys_reg(vcpu, ZCR_EL1) = read_sysreg_el1(SYS_ZCR); - /* Restore the VL that was saved when bound to the CPU */ + /* + * Restore the VL that was saved when bound to the CPU, + * which is the maximum VL for the guest. Because the + * layout of the data when saving the sve state depends + * on the VL, we need to use a consistent (i.e., the + * maximum) VL. + * Note that this means that at guest exit ZCR_EL1 is + * not necessarily the same as on guest entry. + * + * Restoring the VL isn't needed in VHE mode since + * ZCR_EL2 (accessed via ZCR_EL1) would fulfill the same + * role when doing the save from EL2. + */ if (!has_vhe()) sve_cond_update_zcr_vq(vcpu_sve_max_vq(vcpu) - 1, SYS_ZCR_EL1); } + /* + * Flush (save and invalidate) the fpsimd/sve state so that if + * the host tries to use fpsimd/sve, it's not using stale data + * from the guest. + * + * Flushing the state sets the TIF_FOREIGN_FPSTATE bit for the + * context unconditionally, in both nVHE and VHE. This allows + * the kernel to restore the fpsimd/sve state, including ZCR_EL1 + * when needed. + */ fpsimd_save_and_flush_cpu_state(); } else if (has_vhe() && system_supports_sve()) { /* |