Patch "KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state" has been added to the 6.6-stable tree
gregkh at linuxfoundation.org
gregkh at linuxfoundation.org
Tue Mar 25 04:28:56 PDT 2025
This is a note to let you know that I've just added the patch titled
KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
kvm-arm64-unconditionally-save-flush-host-fpsimd-sve-sme-state.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable at vger.kernel.org> know about it.
>From stable+bounces-125720-greg=kroah.com at vger.kernel.org Thu Mar 20 20:18:53 2025
From: Mark Brown <broonie at kernel.org>
Date: Fri, 21 Mar 2025 00:16:02 +0000
Subject: KVM: arm64: Unconditionally save+flush host FPSIMD/SVE/SME state
To: Greg Kroah-Hartman <gregkh at linuxfoundation.org>, Marc Zyngier <maz at kernel.org>, Oliver Upton <oliver.upton at linux.dev>, James Morse <james.morse at arm.com>, Suzuki K Poulose <suzuki.poulose at arm.com>, Catalin Marinas <catalin.marinas at arm.com>, Will Deacon <will at kernel.org>
Cc: linux-arm-kernel at lists.infradead.org, kvmarm at lists.linux.dev, linux-kernel at vger.kernel.org, stable at vger.kernel.org, Mark Brown <broonie at kernel.org>, Mark Rutland <mark.rutland at arm.com>, Eric Auger <eauger at redhat.com>, Wilco Dijkstra <wilco.dijkstra at arm.com>, Eric Auger <eric.auger at redhat.com>, Florian Weimer <fweimer at redhat.com>, Fuad Tabba <tabba at google.com>, Jeremy Linton <jeremy.linton at arm.com>, Paolo Bonzini <pbonzini at redhat.com>
Message-ID: <20250321-stable-sve-6-6-v1-2-0b3a6a14ea53 at kernel.org>
From: Mark Rutland <mark.rutland at arm.com>
[ Upstream commit fbc7e61195e23f744814e78524b73b59faa54ab4 ]
There are several problems with the way hyp code lazily saves the host's
FPSIMD/SVE state, including:
* Host SVE being discarded unexpectedly due to inconsistent
configuration of TIF_SVE and CPACR_ELx.ZEN. This has been seen to
result in QEMU crashes where SVE is used by memmove(), as reported by
Eric Auger:
https://issues.redhat.com/browse/RHEL-68997
* Host SVE state is discarded *after* modification by ptrace, which was an
unintentional ptrace ABI change introduced with lazy discarding of SVE state.
* The host FPMR value can be discarded when running a non-protected VM,
where FPMR support is not exposed to a VM, and that VM uses
FPSIMD/SVE. In these cases the hyp code does not save the host's FPMR
before unbinding the host's FPSIMD/SVE/SME state, leaving a stale
value in memory.
Avoid these by eagerly saving and "flushing" the host's FPSIMD/SVE/SME
state when loading a vCPU such that KVM does not need to save any of the
host's FPSIMD/SVE/SME state. For clarity, fpsimd_kvm_prepare() is
removed and the necessary call to fpsimd_save_and_flush_cpu_state() is
placed in kvm_arch_vcpu_load_fp(). As 'fpsimd_state' and 'fpmr_ptr'
should not be used, they are set to NULL; all uses of these will be
removed in subsequent patches.
Historical problems go back at least as far as v5.17, e.g. erroneous
assumptions about TIF_SVE being clear in commit:
8383741ab2e773a9 ("KVM: arm64: Get rid of host SVE tracking/saving")
... and so this eager save+flush probably needs to be backported to ALL
stable trees.
Fixes: 93ae6b01bafee8fa ("KVM: arm64: Discard any SVE state when entering KVM guests")
Fixes: 8c845e2731041f0f ("arm64/sve: Leave SVE enabled on syscall if we don't context switch")
Fixes: ef3be86021c3bdf3 ("KVM: arm64: Add save/restore support for FPMR")
Reported-by: Eric Auger <eauger at redhat.com>
Reported-by: Wilco Dijkstra <wilco.dijkstra at arm.com>
Reviewed-by: Mark Brown <broonie at kernel.org>
Tested-by: Mark Brown <broonie at kernel.org>
Tested-by: Eric Auger <eric.auger at redhat.com>
Acked-by: Will Deacon <will at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Florian Weimer <fweimer at redhat.com>
Cc: Fuad Tabba <tabba at google.com>
Cc: Jeremy Linton <jeremy.linton at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Oliver Upton <oliver.upton at linux.dev>
Cc: Paolo Bonzini <pbonzini at redhat.com>
Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Reviewed-by: Oliver Upton <oliver.upton at linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-2-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz at kernel.org>
[ Mark: Handle vcpu/host flag conflict ]
Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Signed-off-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
arch/arm64/kernel/fpsimd.c | 25 -------------------------
arch/arm64/kvm/fpsimd.c | 31 ++++++++-----------------------
2 files changed, 8 insertions(+), 48 deletions(-)
--- a/arch/arm64/kernel/fpsimd.c
+++ b/arch/arm64/kernel/fpsimd.c
@@ -1708,31 +1708,6 @@ void fpsimd_signal_preserve_current_stat
}
/*
- * Called by KVM when entering the guest.
- */
-void fpsimd_kvm_prepare(void)
-{
- if (!system_supports_sve())
- return;
-
- /*
- * KVM does not save host SVE state since we can only enter
- * the guest from a syscall so the ABI means that only the
- * non-saved SVE state needs to be saved. If we have left
- * SVE enabled for performance reasons then update the task
- * state to be FPSIMD only.
- */
- get_cpu_fpsimd_context();
-
- if (test_and_clear_thread_flag(TIF_SVE)) {
- sve_to_fpsimd(current);
- current->thread.fp_type = FP_STATE_FPSIMD;
- }
-
- put_cpu_fpsimd_context();
-}
-
-/*
* Associate current's FPSIMD context with this cpu
* The caller must have ownership of the cpu FPSIMD context before calling
* this function.
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -79,14 +79,16 @@ void kvm_arch_vcpu_load_fp(struct kvm_vc
if (!system_supports_fpsimd())
return;
- fpsimd_kvm_prepare();
-
/*
- * We will check TIF_FOREIGN_FPSTATE just before entering the
- * guest in kvm_arch_vcpu_ctxflush_fp() and override this to
- * FP_STATE_FREE if the flag set.
+ * Ensure that any host FPSIMD/SVE/SME state is saved and unbound such
+ * that the host kernel is responsible for restoring this state upon
+ * return to userspace, and the hyp code doesn't need to save anything.
+ *
+ * When the host may use SME, fpsimd_save_and_flush_cpu_state() ensures
+ * that PSTATE.{SM,ZA} == {0,0}.
*/
- vcpu->arch.fp_state = FP_STATE_HOST_OWNED;
+ fpsimd_save_and_flush_cpu_state();
+ vcpu->arch.fp_state = FP_STATE_FREE;
vcpu_clear_flag(vcpu, HOST_SVE_ENABLED);
if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
@@ -96,23 +98,6 @@ void kvm_arch_vcpu_load_fp(struct kvm_vc
vcpu_clear_flag(vcpu, HOST_SME_ENABLED);
if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
vcpu_set_flag(vcpu, HOST_SME_ENABLED);
-
- /*
- * If PSTATE.SM is enabled then save any pending FP
- * state and disable PSTATE.SM. If we leave PSTATE.SM
- * enabled and the guest does not enable SME via
- * CPACR_EL1.SMEN then operations that should be valid
- * may generate SME traps from EL1 to EL1 which we
- * can't intercept and which would confuse the guest.
- *
- * Do the same for PSTATE.ZA in the case where there
- * is state in the registers which has not already
- * been saved, this is very unlikely to happen.
- */
- if (read_sysreg_s(SYS_SVCR) & (SVCR_SM_MASK | SVCR_ZA_MASK)) {
- vcpu->arch.fp_state = FP_STATE_FREE;
- fpsimd_save_and_flush_cpu_state();
- }
}
}
Patches currently in stable-queue which might be from broonie at kernel.org are
queue-6.6/kvm-arm64-calculate-cptr_el2-traps-on-activating-traps.patch
queue-6.6/regulator-check-that-dummy-regulator-has-been-probed-before-using-it.patch
queue-6.6/kvm-arm64-eagerly-switch-zcr_el-1-2.patch
queue-6.6/kvm-arm64-mark-some-header-functions-as-inline.patch
queue-6.6/kvm-arm64-remove-host-fpsimd-saving-for-non-protected-kvm.patch
queue-6.6/regulator-dummy-force-synchronous-probing.patch
queue-6.6/kvm-arm64-refactor-exit-handlers.patch
queue-6.6/kvm-arm64-unconditionally-save-flush-host-fpsimd-sve-sme-state.patch
queue-6.6/kvm-arm64-remove-vhe-host-restore-of-cpacr_el1.smen.patch
queue-6.6/kvm-arm64-remove-vhe-host-restore-of-cpacr_el1.zen.patch
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