On 2026/7/16 下午12:46, Tao Cui wrote:
在 2026/7/16 09:38, Bibo Mao 写道:
Now pv_feature can be set only once, there is problem with VM migration.
Where it is set when vCPU is created and after migration, here it is
allow to set for many times, until vCPU starts to run.
Hi Bibo,
The Sashiko AI review raised two concerns on this patch that I think
are valid:
1. Since ran_atleast_once is per-vCPU but pv_features is VM-wide,
userspace could run vCPU 0 and then use vCPU 1 (whose
ran_atleast_once is still false) to change pv_features while
vCPU 0 is executing.
2. Without the old LOONGARCH_PV_FEAT_UPDATED latch, setting different
PV features on different un-run vCPUs silently overwrites
pv_features instead of returning -EINVAL.
Both stem from using a per-vCPU flag to protect VM-wide state.
Would a VM-level bool in kvm_arch (e.g. pv_features_configured),
set on first SET_ATTR or first RUN of any vCPU, work? It would
not be migrated since it is not exposed via any ioctl.
Now pv_features is per VM, will set it as per CPU to avoid access
contention in next version. Consistent checking should with per CPU
pv_features will be done in VMM, rather than KVM, similar with per CPU
cpucfg feature.
Regards
Bibo Mao
Thanks,
Tao
Signed-off-by: Bibo Mao <[email protected]>
---
arch/loongarch/include/asm/kvm_host.h | 4 +++-
arch/loongarch/kvm/vcpu.c | 15 +++++++++++----
2 files changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/loongarch/include/asm/kvm_host.h
b/arch/loongarch/include/asm/kvm_host.h
index 23cfbecebbd7..af376fc44c44 100644
--- a/arch/loongarch/include/asm/kvm_host.h
+++ b/arch/loongarch/include/asm/kvm_host.h
@@ -163,7 +163,6 @@ enum emulation_result {
#define KVM_LARCH_SWCSR_LATEST (0x1 << 3)
#define KVM_LARCH_HWCSR_USABLE (0x1 << 4)
-#define LOONGARCH_PV_FEAT_UPDATED BIT_ULL(63)
#define LOONGARCH_PV_FEAT_MASK (BIT(KVM_FEATURE_IPI) |
\
BIT(KVM_FEATURE_PREEMPT) | \
BIT(KVM_FEATURE_STEAL_TIME) | \
@@ -250,6 +249,9 @@ struct kvm_vcpu_arch {
/* cpucfg */
u32 cpucfg[KVM_MAX_CPUCFG_REGS];
+ /* VCPU ran at least once */
+ bool ran_atleast_once;
+
/* paravirt steal time */
struct {
u64 guest_addr;
diff --git a/arch/loongarch/kvm/vcpu.c b/arch/loongarch/kvm/vcpu.c
index 20c207d80e31..ce6a1b06d50d 100644
--- a/arch/loongarch/kvm/vcpu.c
+++ b/arch/loongarch/kvm/vcpu.c
@@ -1164,11 +1164,14 @@ static int kvm_loongarch_cpucfg_set_attr(struct
kvm_vcpu *vcpu,
if (val & ~valid)
return -EINVAL;
- /* All vCPUs need set the same PV features */
- if ((kvm->arch.pv_features & LOONGARCH_PV_FEAT_UPDATED)
- && ((kvm->arch.pv_features & valid) != val))
+ if ((kvm->arch.pv_features & valid) == val)
+ return 0;
+
+ if (vcpu->arch.ran_atleast_once)
return -EINVAL;
- kvm->arch.pv_features = val | LOONGARCH_PV_FEAT_UPDATED;
+
+ /* All vCPUs need set the same PV features */
+ kvm->arch.pv_features = val;
return 0;
default:
return -ENXIO;
@@ -1851,6 +1854,10 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
int r = -EINTR;
struct kvm_run *run = vcpu->run;
+ /* Mark this VCPU ran at least once */
+ if (!vcpu->arch.ran_atleast_once)
+ vcpu->arch.ran_atleast_once = true;
+
if (vcpu->mmio_needed) {
if (!vcpu->mmio_is_write)
kvm_complete_mmio_read(vcpu, run);
base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
