| Message ID | 20240730-kvm-arm64-sme-assert-v3-1-8699454e5cb8@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] KVM: arm64: Fix confusion in documentation for pKVM SME assert | expand |
On Tue, Jul 30, 2024 at 02:33:03PM +0100, Mark Brown wrote: > As raised in the review comments for the original patch the assert and > comment added in afb91f5f8ad7 ("KVM: arm64: Ensure that SME controls are > disabled in protected mode") are bogus. The comments says that we check > that we do not have SME enabled for a pKVM guest but the assert actually > checks to see if the host has anything set in SVCR which is unrelated to > the guest features or state, regardless of if those guests are protected > or not. This check is also made in the hypervisor, it will refuse to run > a guest if the check fails, so it appears that the assert here is > intended to improve diagnostics. This hasn't had any feedback for a whole release cycle - are there any issues with the patch? > Fixes: afb91f5f8ad7 ("KVM: arm64: Ensure that SME controls are disabled in protected mode") > Reviewed-by: Fuad Tabba <tabba@google.com> > Signed-off-by: Mark Brown <broonie@kernel.org> Faud reviewed it during the prior cycle.
diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index c53e5b14038d..8eca6b338bb2 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -92,11 +92,14 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu) } /* - * If normal guests gain SME support, maintain this behavior for pKVM - * guests, which don't support SME. + * The pKVM hypervisor does not yet understand how to save or + * restore SME state for the host so double check that if we + * are running with pKVM we have disabled SME. The hypervisor + * enforces this when the guest is run, this check is for + * clearer diagnostics. */ - WARN_ON(is_protected_kvm_enabled() && system_supports_sme() && - read_sysreg_s(SYS_SVCR)); + WARN_ON_ONCE(is_protected_kvm_enabled() && system_supports_sme() && + read_sysreg_s(SYS_SVCR)); } /*
As raised in the review comments for the original patch the assert and comment added in afb91f5f8ad7 ("KVM: arm64: Ensure that SME controls are disabled in protected mode") are bogus. The comments says that we check that we do not have SME enabled for a pKVM guest but the assert actually checks to see if the host has anything set in SVCR which is unrelated to the guest features or state, regardless of if those guests are protected or not. This check is also made in the hypervisor, it will refuse to run a guest if the check fails, so it appears that the assert here is intended to improve diagnostics. Update the comment to reflect the check in the code, and to clarify that we do actually enforce this in the hypervisor. While we're here also update to use a WARN_ON_ONCE() to avoid log spam if this triggers. Fixes: afb91f5f8ad7 ("KVM: arm64: Ensure that SME controls are disabled in protected mode") Reviewed-by: Fuad Tabba <tabba@google.com> Signed-off-by: Mark Brown <broonie@kernel.org> --- Changes in v3: - Rebase onto v6.11-rc1. - Link to v2: https://lore.kernel.org/r/20240605-kvm-arm64-sme-assert-v2-1-54391b0032f4@kernel.org Changes in v2: - Commit message tweaks. - Change the assert to WARN_ON_ONCE(). - Link to v1: https://lore.kernel.org/r/20240604-kvm-arm64-sme-assert-v1-1-5d98348d00f8@kernel.org --- arch/arm64/kvm/fpsimd.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) --- base-commit: 8400291e289ee6b2bf9779ff1c83a291501f017b change-id: 20240604-kvm-arm64-sme-assert-5ad755d4e8a6 Best regards,