Re: [PATCH v9 20/22] RISC-V: KVM: Fix race-condition in kvm_riscv_vcpu_sync_interrupts()

[Anup Patel]

On Mon, Oct 21, 2019 at 10:57 PM Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 16/10/19 18:12, Anup Patel wrote:
> > +     /* 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);
> > +             }
>
> Looks good, but I wonder if this could just be "csr->vsip =
> csr_read(CSR_VSIP)", which will be fixed up by flush_interrupts on the
> next entry.

It's not just "csr->vsip = csr_read(CSR_VSIP" because "irqs_pending"
bitmap has to be in-sync with Guest updates to VSIP because WFI
trap-n-emulate will check for pending interrupts which in-turn checks
"irqs_pending" bitmap.

Regards,
Anup