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KVM: RISC-V: Clear former VCPU cache on virtualization disable

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When a CPU is taken offline or enters deep idle states, hypervisor CSR
state is lost. The kvm_former_vcpu fast-path optimization caches the
last VCPU that ran on each CPU to avoid expensive CSR restoration when
the same VCPU is re-scheduled on the same CPU. However, if this cache
is not cleared when CSR state is lost, the next VCPU entry will
incorrectly skip CSR restoration, leading to corrupt hypervisor state.

Add kvm_riscv_clear_former_vcpu() to invalidate the per-CPU cache and
call it from kvm_arch_disable_virtualization_cpu() to ensure proper CSR
restoration after CPU offline or system suspend events.

Fixes: 1323a5cfe5 ("KVM: riscv: Skip CSR restore if VCPU is reloaded on the same core")
Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
Reviewed-by: Nutty Liu <nutty.liu@hotmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/r/20260721-kvm-cpu-pm-v4-1-146bf942547d@sifive.com
Signed-off-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Yong-Xuan Wang 2026-07-21 22:52:02 -07:00 committed by Anup Patel
parent 735bc20c24
commit dfdf1374fd
3 changed files with 15 additions and 0 deletions
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2
arch/riscv/include/asm/kvm_host.h
View File

@ -290,6 +290,8 @@ static inline bool kvm_arch_pmi_in_guest(struct kvm_vcpu *vcpu)
static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
void kvm_riscv_clear_former_vcpu(void);
int kvm_riscv_setup_default_irq_routing(struct kvm *kvm, u32 lines);
void __kvm_riscv_unpriv_trap(void);

2
arch/riscv/kvm/main.c
View File

@ -69,6 +69,8 @@ void kvm_arch_disable_virtualization_cpu(void)
csr_write(CSR_HEDELEG, 0);
csr_write(CSR_HIDELEG, 0);
kvm_riscv_clear_former_vcpu();
kvm_riscv_nacl_disable();
}

11
arch/riscv/kvm/vcpu.c
View File

@ -26,6 +26,17 @@
static DEFINE_PER_CPU(struct kvm_vcpu *, kvm_former_vcpu);
void kvm_riscv_clear_former_vcpu(void)
{
/*
* Clear the per-CPU former VCPU pointer because hypervisor CSR state
* will be lost. This ensures that the next VCPU entry will properly
* restore all CSRs instead of incorrectly skipping CSR restoration
* via the fast-path optimization.
*/
__this_cpu_write(kvm_former_vcpu, NULL);
}
const struct kvm_stats_desc kvm_vcpu_stats_desc[] = {
KVM_GENERIC_VCPU_STATS(),
STATS_DESC_COUNTER(VCPU, ecall_exit_stat),