JIRA: https://issues.redhat.com/browse/RHEL-82298
In non-protected KVM modes, while the guest FPSIMD/SVE/SME state is live on the
CPU, the host's active SVE VL may differ from the guest's maximum SVE VL:
* For VHE hosts, when a VM uses NV, ZCR_EL2 contains a value constrained
by the guest hypervisor, which may be less than or equal to that
guest's maximum VL.
Note: in this case the value of ZCR_EL1 is immaterial due to E2H.
* For nVHE/hVHE hosts, ZCR_EL1 contains a value written by the guest,
which may be less than or greater than the guest's maximum VL.
Note: in this case hyp code traps host SVE usage and lazily restores
ZCR_EL2 to the host's maximum VL, which may be greater than the
guest's maximum VL.
This can be the case between exiting a guest and kvm_arch_vcpu_put_fp().
If a softirq is taken during this period and the softirq handler tries
to use kernel-mode NEON, then the kernel will fail to save the guest's
FPSIMD/SVE state, and will pend a SIGKILL for the current thread.
This happens because kvm_arch_vcpu_ctxsync_fp() binds the guest's live
FPSIMD/SVE state with the guest's maximum SVE VL, and
fpsimd_save_user_state() verifies that the live SVE VL is as expected
before attempting to save the register state:
| if (WARN_ON(sve_get_vl() != vl)) {
| force_signal_inject(SIGKILL, SI_KERNEL, 0, 0);
| return;
| }
Fix this and make this a bit easier to reason about by always eagerly
switching ZCR_EL{1,2} at hyp during guest<->host transitions. With this
happening, there's no need to trap host SVE usage, and the nVHE/nVHE
__deactivate_cptr_traps() logic can be simplified to enable host access
to all present FPSIMD/SVE/SME features.
In protected nVHE/hVHE modes, the host's state is always saved/restored
by hyp, and the guest's state is saved prior to exit to the host, so
from the host's PoV the guest never has live FPSIMD/SVE/SME state, and
the host's ZCR_EL1 is never clobbered by hyp.
Fixes: 8c8010d69c ("KVM: arm64: Save/restore SVE state for nVHE")
Fixes: 2e3cf82063a00ea0 ("KVM: arm64: nv: Ensure correct VL is loaded before saving SVE state")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-9-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
(cherry picked from commit 59419f10045bc955d2229819c7cf7a8b0b9c5b59)
Signed-off-by: Gavin Shan <gshan@redhat.com>
Conflicts:
arch/arm64/kvm/hyp/nvhe/hyp-main.c
Conflict due to missed upstream commit f7d03fcbf1f4 ("KVM: arm64:
Introduce __pkvm_vcpu_{load,put}()") where the variable (host_vcpu)
corresponding to the vCPU instance in the hypervisor linear mapping
adress is removed. Without the commit, the variable is still available
and usable. Contextual conflict due to missed upstream commit
e5ecedcd7cc2 ("arm64/sysreg: Get rid of CPACR_ELx SysregFields")
where CPACR_ELx_ZEN is renamed to CPACR_EL1_ZEN in handle_trap().
The whole chunk related to SVE trap handling is removed anyway.
arch/arm64/kvm/hyp/nvhe/switch.c
Conflict due to missed upstream commit ee14db31a9c84 ("KVM: arm64:
Refactor CPTR trap deactivation") where kvm_reset_cptr_el2() is
renamed to __deactivate_cptr_traps(). Apply the changes for
__deactivate_cptr_traps() to kvm_reset_cptr_el2().
939b18635e