Looks good.
Reviewed-by: Caleb Schlossin <cal...@linux.ibm.com>
On 5/11/25 10:10 PM, Nicholas Piggin wrote:
> The group interrupt delivery flow selects the group backlog scan if
> LSMFB < IPB, but that scan may find an interrupt with a priority >=
> IPB. In that case, the VP-direct interrupt should be chosen. This
> extends to selecting the lowest prio between POOL and PHYS rings.
>
> Implement this just by re-starting the selection logic if the
> backlog irq was not found or priority did not match LSMFB (LSMFB
> is updated so next time around it would see the right value and
> not loop infinitely).
>
> Signed-off-by: Nicholas Piggin <npig...@gmail.com>
> ---
> hw/intc/xive2.c | 32 ++++++++++++++++++++++----------
> 1 file changed, 22 insertions(+), 10 deletions(-)
>
> diff --git a/hw/intc/xive2.c b/hw/intc/xive2.c
> index 8ede95b671..de139dcfbf 100644
> --- a/hw/intc/xive2.c
> +++ b/hw/intc/xive2.c
> @@ -939,7 +939,7 @@ static void xive2_tctx_set_cppr(XiveTCTX *tctx, uint8_t
> ring, uint8_t cppr)
> {
> uint8_t *regs = &tctx->regs[ring];
> Xive2Router *xrtr = XIVE2_ROUTER(tctx->xptr);
> - uint8_t old_cppr, backlog_prio, first_group, group_level = 0;
> + uint8_t old_cppr, backlog_prio, first_group, group_level;
> uint8_t pipr_min, lsmfb_min, ring_min;
> bool group_enabled;
> uint32_t nvp_blk, nvp_idx;
> @@ -961,10 +961,12 @@ static void xive2_tctx_set_cppr(XiveTCTX *tctx, uint8_t
> ring, uint8_t cppr)
> * Recompute the PIPR based on local pending interrupts. It will
> * be adjusted below if needed in case of pending group interrupts.
> */
> +again:
> pipr_min = xive_ipb_to_pipr(regs[TM_IPB]);
> group_enabled = !!regs[TM_LGS];
> - lsmfb_min = (group_enabled) ? regs[TM_LSMFB] : 0xff;
> + lsmfb_min = group_enabled ? regs[TM_LSMFB] : 0xff;
> ring_min = ring;
> + group_level = 0;
>
> /* PHYS updates also depend on POOL values */
> if (ring == TM_QW3_HV_PHYS) {
> @@ -998,9 +1000,6 @@ static void xive2_tctx_set_cppr(XiveTCTX *tctx, uint8_t
> ring, uint8_t cppr)
> }
> }
>
> - /* PIPR should not be set to a value greater than CPPR */
> - regs[TM_PIPR] = (pipr_min > cppr) ? cppr : pipr_min;
> -
> rc = xive2_tctx_get_nvp_indexes(tctx, ring_min, &nvp_blk, &nvp_idx);
> if (rc) {
> qemu_log_mask(LOG_GUEST_ERROR, "XIVE: set CPPR on invalid
> context\n");
> @@ -1019,7 +1018,7 @@ static void xive2_tctx_set_cppr(XiveTCTX *tctx, uint8_t
> ring, uint8_t cppr)
>
> if (group_enabled &&
> lsmfb_min < cppr &&
> - lsmfb_min < regs[TM_PIPR]) {
> + lsmfb_min < pipr_min) {
> /*
> * Thread has seen a group interrupt with a higher priority
> * than the new cppr or pending local interrupt. Check the
> @@ -1048,12 +1047,25 @@ static void xive2_tctx_set_cppr(XiveTCTX *tctx,
> uint8_t ring, uint8_t cppr)
> nvp_blk, nvp_idx,
> first_group,
> &group_level);
> tctx->regs[ring_min + TM_LSMFB] = backlog_prio;
> - if (backlog_prio != 0xFF) {
> - xive2_presenter_backlog_decr(tctx->xptr, nvp_blk, nvp_idx,
> - backlog_prio, group_level);
> - regs[TM_PIPR] = backlog_prio;
> + if (backlog_prio != lsmfb_min) {
> + /*
> + * If the group backlog scan finds a less favored or no
> interrupt,
> + * then re-do the processing which may turn up a more favored
> + * interrupt from IPB or the other pool. Backlog should not
> + * find a priority < LSMFB.
> + */
> + g_assert(backlog_prio >= lsmfb_min);
> + goto again;
> }
> +
> + xive2_presenter_backlog_decr(tctx->xptr, nvp_blk, nvp_idx,
> + backlog_prio, group_level);
> + pipr_min = backlog_prio;
> }
> +
> + /* PIPR should not be set to a value greater than CPPR */
> + regs[TM_PIPR] = (pipr_min > cppr) ? cppr : pipr_min;
> +
> /* CPPR has changed, check if we need to raise a pending exception */
> xive_tctx_notify(tctx, ring_min, group_level);
> }
