Patch "KVM: arm64: Eagerly switch ZCR_EL{1,2}" has been added to the 6.6-stable tree
gregkh at linuxfoundation.org
gregkh at linuxfoundation.org
Tue Mar 25 04:28:55 PDT 2025
This is a note to let you know that I've just added the patch titled
KVM: arm64: Eagerly switch ZCR_EL{1,2}
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-eagerly-switch-zcr_el-1-2.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 broonie at kernel.org Thu Mar 20 20:18:40 2025
From: Mark Brown <broonie at kernel.org>
Date: Fri, 21 Mar 2025 00:16:08 +0000
Subject: KVM: arm64: Eagerly switch ZCR_EL{1,2}
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>, Fuad Tabba <tabba at google.com>
Message-ID: <20250321-stable-sve-6-6-v1-8-0b3a6a14ea53 at kernel.org>
From: Mark Rutland <mark.rutland at arm.com>
[ Upstream commit 59419f10045bc955d2229819c7cf7a8b0b9c5b59 ]
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: 8c8010d69c132273 ("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 at arm.com>
Reviewed-by: Mark Brown <broonie at kernel.org>
Tested-by: Mark Brown <broonie at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Fuad Tabba <tabba at google.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Oliver Upton <oliver.upton at linux.dev>
Cc: Will Deacon <will at kernel.org>
Reviewed-by: Oliver Upton <oliver.upton at linux.dev>
Link: https://lore.kernel.org/r/20250210195226.1215254-9-mark.rutland@arm.com
Signed-off-by: Marc Zyngier <maz at kernel.org>
[ v6.6 lacks pKVM saving of host SVE state, pull in discovery of maximum
host VL separately -- broonie ]
Signed-off-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
---
arch/arm64/include/asm/kvm_host.h | 1
arch/arm64/include/asm/kvm_hyp.h | 1
arch/arm64/kvm/fpsimd.c | 19 +++++------
arch/arm64/kvm/hyp/entry.S | 5 ++
arch/arm64/kvm/hyp/include/hyp/switch.h | 55 ++++++++++++++++++++++++++++++++
arch/arm64/kvm/hyp/nvhe/hyp-main.c | 12 +-----
arch/arm64/kvm/hyp/nvhe/pkvm.c | 2 +
arch/arm64/kvm/hyp/nvhe/switch.c | 33 ++++++++++++++++---
arch/arm64/kvm/hyp/vhe/switch.c | 4 ++
arch/arm64/kvm/reset.c | 3 +
10 files changed, 113 insertions(+), 22 deletions(-)
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -73,6 +73,7 @@ static inline enum kvm_mode kvm_get_mode
#endif
extern unsigned int __ro_after_init kvm_sve_max_vl;
+extern unsigned int __ro_after_init kvm_host_sve_max_vl;
int __init kvm_arm_init_sve(void);
u32 __attribute_const__ kvm_target_cpu(void);
--- a/arch/arm64/include/asm/kvm_hyp.h
+++ b/arch/arm64/include/asm/kvm_hyp.h
@@ -145,5 +145,6 @@ extern u64 kvm_nvhe_sym(id_aa64smfr0_el1
extern unsigned long kvm_nvhe_sym(__icache_flags);
extern unsigned int kvm_nvhe_sym(kvm_arm_vmid_bits);
+extern unsigned int kvm_nvhe_sym(kvm_host_sve_max_vl);
#endif /* __ARM64_KVM_HYP_H__ */
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -152,15 +152,16 @@ void kvm_arch_vcpu_put_fp(struct kvm_vcp
local_irq_save(flags);
if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED) {
- 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 */
- 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();
}
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -44,6 +44,11 @@ alternative_if ARM64_HAS_RAS_EXTN
alternative_else_nop_endif
mrs x1, isr_el1
cbz x1, 1f
+
+ // Ensure that __guest_enter() always provides a context
+ // synchronization event so that callers don't need ISBs for anything
+ // that would usually be synchonized by the ERET.
+ isb
mov x0, #ARM_EXCEPTION_IRQ
ret
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -273,6 +273,61 @@ static inline void __hyp_sve_restore_gue
write_sysreg_el1(__vcpu_sys_reg(vcpu, ZCR_EL1), SYS_ZCR);
}
+static inline void fpsimd_lazy_switch_to_guest(struct kvm_vcpu *vcpu)
+{
+ u64 zcr_el1, zcr_el2;
+
+ if (!guest_owns_fp_regs(vcpu))
+ return;
+
+ if (vcpu_has_sve(vcpu)) {
+ zcr_el2 = vcpu_sve_max_vq(vcpu) - 1;
+
+ write_sysreg_el2(zcr_el2, SYS_ZCR);
+
+ zcr_el1 = __vcpu_sys_reg(vcpu, ZCR_EL1);
+ write_sysreg_el1(zcr_el1, SYS_ZCR);
+ }
+}
+
+static inline void fpsimd_lazy_switch_to_host(struct kvm_vcpu *vcpu)
+{
+ u64 zcr_el1, zcr_el2;
+
+ if (!guest_owns_fp_regs(vcpu))
+ return;
+
+ /*
+ * When the guest owns the FP regs, we know that guest+hyp traps for
+ * any FPSIMD/SVE/SME features exposed to the guest have been disabled
+ * by either fpsimd_lazy_switch_to_guest() or kvm_hyp_handle_fpsimd()
+ * prior to __guest_entry(). As __guest_entry() guarantees a context
+ * synchronization event, we don't need an ISB here to avoid taking
+ * traps for anything that was exposed to the guest.
+ */
+ if (vcpu_has_sve(vcpu)) {
+ zcr_el1 = read_sysreg_el1(SYS_ZCR);
+ __vcpu_sys_reg(vcpu, ZCR_EL1) = zcr_el1;
+
+ /*
+ * The guest's state is always saved using the guest's max VL.
+ * Ensure that the host has the guest's max VL active such that
+ * the host can save the guest's state lazily, but don't
+ * artificially restrict the host to the guest's max VL.
+ */
+ if (has_vhe()) {
+ zcr_el2 = vcpu_sve_max_vq(vcpu) - 1;
+ write_sysreg_el2(zcr_el2, SYS_ZCR);
+ } else {
+ zcr_el2 = sve_vq_from_vl(kvm_host_sve_max_vl) - 1;
+ write_sysreg_el2(zcr_el2, SYS_ZCR);
+
+ zcr_el1 = vcpu_sve_max_vq(vcpu) - 1;
+ write_sysreg_el1(zcr_el1, SYS_ZCR);
+ }
+ }
+}
+
/*
* We trap the first access to the FP/SIMD to save the host context and
* restore the guest context lazily.
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -5,6 +5,7 @@
*/
#include <hyp/adjust_pc.h>
+#include <hyp/switch.h>
#include <asm/pgtable-types.h>
#include <asm/kvm_asm.h>
@@ -95,7 +96,9 @@ static void handle___kvm_vcpu_run(struct
pkvm_put_hyp_vcpu(hyp_vcpu);
} else {
/* The host is fully trusted, run its vCPU directly. */
+ fpsimd_lazy_switch_to_guest(host_vcpu);
ret = __kvm_vcpu_run(host_vcpu);
+ fpsimd_lazy_switch_to_host(host_vcpu);
}
out:
@@ -416,15 +419,6 @@ void handle_trap(struct kvm_cpu_context
case ESR_ELx_EC_SMC64:
handle_host_smc(host_ctxt);
break;
- case ESR_ELx_EC_SVE:
- if (has_hvhe())
- sysreg_clear_set(cpacr_el1, 0, (CPACR_EL1_ZEN_EL1EN |
- CPACR_EL1_ZEN_EL0EN));
- else
- sysreg_clear_set(cptr_el2, CPTR_EL2_TZ, 0);
- isb();
- sve_cond_update_zcr_vq(ZCR_ELx_LEN_MASK, SYS_ZCR_EL2);
- break;
case ESR_ELx_EC_IABT_LOW:
case ESR_ELx_EC_DABT_LOW:
handle_host_mem_abort(host_ctxt);
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c
@@ -18,6 +18,8 @@ unsigned long __icache_flags;
/* Used by kvm_get_vttbr(). */
unsigned int kvm_arm_vmid_bits;
+unsigned int kvm_host_sve_max_vl;
+
/*
* Set trap register values based on features in ID_AA64PFR0.
*/
--- a/arch/arm64/kvm/hyp/nvhe/switch.c
+++ b/arch/arm64/kvm/hyp/nvhe/switch.c
@@ -40,6 +40,9 @@ static void __activate_cptr_traps(struct
{
u64 val = CPTR_EL2_TAM; /* Same bit irrespective of E2H */
+ if (!guest_owns_fp_regs(vcpu))
+ __activate_traps_fpsimd32(vcpu);
+
if (has_hvhe()) {
val |= CPACR_ELx_TTA;
@@ -48,6 +51,8 @@ static void __activate_cptr_traps(struct
if (vcpu_has_sve(vcpu))
val |= CPACR_ELx_ZEN;
}
+
+ write_sysreg(val, cpacr_el1);
} else {
val |= CPTR_EL2_TTA | CPTR_NVHE_EL2_RES1;
@@ -62,12 +67,32 @@ static void __activate_cptr_traps(struct
if (!guest_owns_fp_regs(vcpu))
val |= CPTR_EL2_TFP;
+
+ write_sysreg(val, cptr_el2);
}
+}
- if (!guest_owns_fp_regs(vcpu))
- __activate_traps_fpsimd32(vcpu);
+static void __deactivate_cptr_traps(struct kvm_vcpu *vcpu)
+{
+ if (has_hvhe()) {
+ u64 val = CPACR_ELx_FPEN;
+
+ if (cpus_have_final_cap(ARM64_SVE))
+ val |= CPACR_ELx_ZEN;
+ if (cpus_have_final_cap(ARM64_SME))
+ val |= CPACR_ELx_SMEN;
+
+ write_sysreg(val, cpacr_el1);
+ } else {
+ u64 val = CPTR_NVHE_EL2_RES1;
+
+ if (!cpus_have_final_cap(ARM64_SVE))
+ val |= CPTR_EL2_TZ;
+ if (!cpus_have_final_cap(ARM64_SME))
+ val |= CPTR_EL2_TSM;
- kvm_write_cptr_el2(val);
+ write_sysreg(val, cptr_el2);
+ }
}
static void __activate_traps(struct kvm_vcpu *vcpu)
@@ -120,7 +145,7 @@ static void __deactivate_traps(struct kv
write_sysreg(this_cpu_ptr(&kvm_init_params)->hcr_el2, hcr_el2);
- kvm_reset_cptr_el2(vcpu);
+ __deactivate_cptr_traps(vcpu);
write_sysreg(__kvm_hyp_host_vector, vbar_el2);
}
--- a/arch/arm64/kvm/hyp/vhe/switch.c
+++ b/arch/arm64/kvm/hyp/vhe/switch.c
@@ -212,6 +212,8 @@ static int __kvm_vcpu_run_vhe(struct kvm
sysreg_save_host_state_vhe(host_ctxt);
+ fpsimd_lazy_switch_to_guest(vcpu);
+
/*
* ARM erratum 1165522 requires us to configure both stage 1 and
* stage 2 translation for the guest context before we clear
@@ -247,6 +249,8 @@ static int __kvm_vcpu_run_vhe(struct kvm
__deactivate_traps(vcpu);
+ fpsimd_lazy_switch_to_host(vcpu);
+
sysreg_restore_host_state_vhe(host_ctxt);
if (vcpu->arch.fp_state == FP_STATE_GUEST_OWNED)
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -46,11 +46,14 @@ static u32 __ro_after_init kvm_ipa_limit
PSR_AA32_I_BIT | PSR_AA32_F_BIT)
unsigned int __ro_after_init kvm_sve_max_vl;
+unsigned int __ro_after_init kvm_host_sve_max_vl;
int __init kvm_arm_init_sve(void)
{
if (system_supports_sve()) {
kvm_sve_max_vl = sve_max_virtualisable_vl();
+ kvm_host_sve_max_vl = sve_max_vl();
+ kvm_nvhe_sym(kvm_host_sve_max_vl) = kvm_host_sve_max_vl;
/*
* The get_sve_reg()/set_sve_reg() ioctl interface will need
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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