On 10/5/18 1:06 pm, Benjamin Herrenschmidt wrote:
> When a vcpu priority (CPPR) is set to a lower value (masking more
> interrupts), we stop processing interrupts already in the queue
> for the priorities that have now been masked.
>
> If those interrupts were previously re-routed to a different
> CPU, they might still be stuck until the older one that has
> them in its queue processes them. In the case of guest CPU
> unplug, that can be never.
>
> To address that without creating additional overhead for
> the normal interrupt processing path, this changes H_CPPR
> handling so that when such a priority change occurs, we
> scan the interrupt queue for that vCPU, and for any
> interrupt in there that has been re-routed, we replace it
> with a dummy and force a re-trigger.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Tested-by: Alexey Kardashevskiy <aik@xxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_xive_template.c | 108 ++++++++++++++++++++++--
> 1 file changed, 101 insertions(+), 7 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_xive_template.c b/arch/powerpc/kvm/book3s_xive_template.c
> index c7a5deadd1cc..99c3620b40d9 100644
> --- a/arch/powerpc/kvm/book3s_xive_template.c
> +++ b/arch/powerpc/kvm/book3s_xive_template.c
> @@ -11,6 +11,9 @@
> #define XGLUE(a,b) a##b
> #define GLUE(a,b) XGLUE(a,b)
>
> +/* Dummy interrupt used when taking interrupts out of a queue in H_CPPR */
> +#define XICS_DUMMY 1
> +
> static void GLUE(X_PFX,ack_pending)(struct kvmppc_xive_vcpu *xc)
> {
> u8 cppr;
> @@ -205,6 +208,10 @@ static u32 GLUE(X_PFX,scan_interrupts)(struct kvmppc_xive_vcpu *xc,
> goto skip_ipi;
> }
>
> + /* If it's the dummy interrupt, continue searching */
> + if (hirq == XICS_DUMMY)
> + goto skip_ipi;
> +
> /* If fetching, update queue pointers */
> if (scan_type == scan_fetch) {
> q->idx = idx;
> @@ -385,9 +392,76 @@ static void GLUE(X_PFX,push_pending_to_hw)(struct kvmppc_xive_vcpu *xc)
> __x_writeb(prio, __x_tima + TM_SPC_SET_OS_PENDING);
> }
>
> +static void GLUE(X_PFX,scan_for_rerouted_irqs)(struct kvmppc_xive *xive,
> + struct kvmppc_xive_vcpu *xc)
> +{
> + unsigned int prio;
> +
> + /* For each priority that is now masked */
> + for (prio = xc->cppr; prio < KVMPPC_XIVE_Q_COUNT; prio++) {
> + struct xive_q *q = &xc->queues[prio];
> + struct kvmppc_xive_irq_state *state;
> + struct kvmppc_xive_src_block *sb;
> + u32 idx, toggle, entry, irq, hw_num;
> + struct xive_irq_data *xd;
> + __be32 *qpage;
> + u16 src;
> +
> + idx = q->idx;
> + toggle = q->toggle;
> + qpage = READ_ONCE(q->qpage);
> + if (!qpage)
> + continue;
> +
> + /* For each interrupt in the queue */
> + for (;;) {
> + entry = be32_to_cpup(qpage + idx);
> +
> + /* No more ? */
> + if ((entry >> 31) == toggle)
> + break;
> + irq = entry & 0x7fffffff;
> +
> + /* Skip dummies and IPIs */
> + if (irq == XICS_DUMMY || irq == XICS_IPI)
> + goto next;
> + sb = kvmppc_xive_find_source(xive, irq, &src);
> + if (!sb)
> + goto next;
> + state = &sb->irq_state[src];
> +
> + /* Has it been rerouted ? */
> + if (xc->server_num == state->act_server)
> + goto next;
> +
> + /*
> + * Allright, it *has* been re-routed, kill it from
> + * the queue.
> + */
> + qpage[idx] = cpu_to_be32((entry & 0x80000000) | XICS_DUMMY);
> +
> + /* Find the HW interrupt */
> + kvmppc_xive_select_irq(state, &hw_num, &xd);
> +
> + /* If it's not an LSI, set PQ to 11 the EOI will force a resend */
> + if (!(xd->flags & XIVE_IRQ_FLAG_LSI))
> + GLUE(X_PFX,esb_load)(xd, XIVE_ESB_SET_PQ_11);
> +
> + /* EOI the source */
> + GLUE(X_PFX,source_eoi)(hw_num, xd);
> +
> + next:
> + idx = (idx + 1) & q->msk;
> + if (idx == 0)
> + toggle ^= 1;
> + }
> + }
> +}
> +
> X_STATIC int GLUE(X_PFX,h_cppr)(struct kvm_vcpu *vcpu, unsigned long cppr)
> {
> struct kvmppc_xive_vcpu *xc = vcpu->arch.xive_vcpu;
> + struct kvmppc_xive *xive = vcpu->kvm->arch.xive;
> u8 old_cppr;
>
> pr_devel("H_CPPR(cppr=%ld)\n", cppr);
> @@ -407,14 +481,34 @@ X_STATIC int GLUE(X_PFX,h_cppr)(struct kvm_vcpu *vcpu, unsigned long cppr)
> */
> smp_mb();
>
> - /*
> - * We are masking less, we need to look for pending things
> - * to deliver and set VP pending bits accordingly to trigger
> - * a new interrupt otherwise we might miss MFRR changes for
> - * which we have optimized out sending an IPI signal.
> - */
> - if (cppr > old_cppr)
> + if (cppr > old_cppr) {
> + /*
> + * We are masking less, we need to look for pending things
> + * to deliver and set VP pending bits accordingly to trigger
> + * a new interrupt otherwise we might miss MFRR changes for
> + * which we have optimized out sending an IPI signal.
> + */
> GLUE(X_PFX,push_pending_to_hw)(xc);
> + } else {
> + /*
> + * We are masking more, we need to check the queue for any
> + * interrupt that has been routed to another CPU, take
> + * it out (replace it with the dummy) and retrigger it.
> + *
> + * This is necessary since those interrupts may otherwise
> + * never be processed, at least not until this CPU restores
> + * its CPPR.
> + *
> + * This is in theory racy vs. HW adding new interrupts to
> + * the queue. In practice this works because the interesting
> + * cases are when the guest has done a set_xive() to move the
> + * interrupt away, which flushes the xive, followed by the
> + * target CPU doing a H_CPPR. So any new interrupt coming into
> + * the queue must still be routed to us and isn't a source
> + * of concern.
> + */
> + GLUE(X_PFX,scan_for_rerouted_irqs)(xive, xc);
> + }
>
> /* Apply new CPPR */
> xc->hw_cppr = cppr;
>
> --
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--
Alexey
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