Re: [PATCH] LoongArch: KVM: Allow to set pv_feature until vCPU run

[Bibo Mao]

On 2026/7/16 下午12:27, Huacai Chen wrote:

Hi, Bibo,

On Thu, Jul 16, 2026 at 9:45 AM Bibo Mao <maob...@loongson.cn> wrote:

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.

Signed-off-by: Bibo Mao <maob...@loongson.cn>
---
  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;

So long a name? Maybe has_run is enough?

well, will use has_run for short.

Regards
Bibo Mao

Huacai

+
         /* 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
--
2.39.3