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Subject[PATCH v9 20/22] RISC-V: KVM: Fix race-condition in kvm_riscv_vcpu_sync_interrupts()
Date
Currently, we sync-up Guest VSIP and VSIE CSRs with HW state upon
VM-exit. This helps us track enable/disable state of interrupts
and VSIP.SSIP bit updates by Guest.

Unfortunately, the implementation of kvm_riscv_vcpu_sync_interrupts()
is racey when running SMP Guest on SMP Host because it can happen
that IRQ_S_SOFT is already queued from other Host CPU and we might
accidentally clear a valid pending IRQ_S_SOFT.

To fix this, we use test_and_set_bit() to update irqs_pending_mask
in kvm_riscv_vcpu_sync_interrupts() instead of directly calling
kvm_riscv_vcpu_set/unset_interrupt() functions.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
---
arch/riscv/kvm/vcpu.c | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index f1a218d3a8cf..844542dd13e4 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -662,15 +662,22 @@ void kvm_riscv_vcpu_flush_interrupts(struct kvm_vcpu *vcpu)

void kvm_riscv_vcpu_sync_interrupts(struct kvm_vcpu *vcpu)
{
- vcpu->arch.guest_csr.vsip = csr_read(CSR_VSIP);
- vcpu->arch.guest_csr.vsie = csr_read(CSR_VSIE);
+ unsigned long vsip;
+ struct kvm_vcpu_arch *v = &vcpu->arch;
+ struct kvm_vcpu_csr *csr = &vcpu->arch.guest_csr;

- /* Guest can directly update VSIP software interrupt bits */
- if (vcpu->arch.guest_csr.vsip ^ READ_ONCE(vcpu->arch.irqs_pending)) {
- if (vcpu->arch.guest_csr.vsip & (1UL << IRQ_S_SOFT))
- kvm_riscv_vcpu_set_interrupt(vcpu, IRQ_S_SOFT);
- else
- kvm_riscv_vcpu_unset_interrupt(vcpu, IRQ_S_SOFT);
+ /* Read current VSIP and VSIE CSRs */
+ vsip = csr_read(CSR_VSIP);
+ csr->vsie = csr_read(CSR_VSIE);
+
+ /* Sync-up VSIP.SSIP bit changes does by Guest */
+ if ((csr->vsip ^ vsip) & (1UL << IRQ_S_SOFT)) {
+ if (!test_and_set_bit(IRQ_S_SOFT, &v->irqs_pending_mask)) {
+ if (vsip & (1UL << IRQ_S_SOFT))
+ set_bit(IRQ_S_SOFT, &v->irqs_pending);
+ else
+ clear_bit(IRQ_S_SOFT, &v->irqs_pending);
+ }
}
}

--
2.17.1
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