Re: [PATCH net v2] bnxt_en: Don't keep MSI-X vectors added before FW reserves them

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- [Medium] In bnxt_reserve_rings()
  (drivers/net/ethernet/broadcom/bnxt/bnxt.c), the new recompute in the…
- [Low] With BNXT_NEW_RM, bnxt_check_rings() now allocates the extra
  dynamic MSI-X vectors only to test availability, then frees them at…

Pre-existing issues:
- [High] bnxt_clear_int_mode() frees the vectors and sets bp->irq_tbl =
  NULL but leaves bp->total_irqs stale.
- [Medium] bnxt_hwrm_check_pf_rings() does not check the return value of
  __bnxt_hwrm_reserve_pf_rings().

--

bnxt_en: Don't keep MSI-X vectors added before FW reserves them

When BNXT_NEW_RM is set, bnxt_check_rings() now frees the dynamically
allocated MSI-X vectors right after the availability check.
bnxt_reserve_rings() then allocates them after __bnxt_reserve_rings(),
sized from bnxt_get_num_msix(). It also grows the vectors when no
reservation is needed but FW already holds one, and clears
irq_tbl[].vector when trimming.

Closes: https://lore.kernel.org/all/20261022193620.2152038-1-vlad.wing@gmail.com/

> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> index 0682060b048ce..55b11c7684313 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c

[ ... ]

> @@ -11701,8 +11702,23 @@ int bnxt_reserve_rings(struct bnxt *bp, bool irq_re_init)
>  	int irqs_required;
>  	int rc;
>  
> -	if (!bnxt_need_reserve_rings(bp))
> +	if (!bnxt_need_reserve_rings(bp)) {
> +		/* FW may already hold the reservation from an earlier
> +		 * reservation that was not followed by growing the dynamic
> +		 * MSI-X vectors, e.g. because the allocation failed.
> +		 */
> +		if (irq_re_init && BNXT_NEW_RM(bp) && bp->irq_tbl &&
> +		    pci_msix_can_alloc_dyn(bp->pdev)) {

[ ... ]

> @@ -11728,6 +11744,10 @@ int bnxt_reserve_rings(struct bnxt *bp, bool irq_re_init)
>  			rc = bnxt_init_int_mode(bp);
>  		bnxt_ulp_irq_restart(bp, rc);
>  	} else if (irq_change && !rc) {
> +		/* Size the vectors from what FW actually reserved, which
> +		 * can be less than what was requested.
> +		 */
> +		irqs_required = bnxt_get_num_msix(bp);

[Severity: Medium]
The comment says this sizes the vectors from what FW actually reserved.
Under BNXT_NEW_RM, though, bnxt_get_num_msix() returns
bnxt_nq_rings_in_use(), which is bp->cp_nr_rings +
bnxt_get_ulp_msix_num(bp). It is not hw_resc->resv_irqs.

Can this still activate unreserved MSI-X entries when the RoCE driver is
registered?

In __bnxt_reserve_rings(), the FW IRQ grant (copied into hwr.cp by
bnxt_copy_reserved_rings()) only bounds the L2 count:

	hwr.cp = min_t(int, hwr.cp, bp->cp_nr_rings);

The re-clamp of the ULP vectors against resv_irqs is skipped when a ULP
is registered:

	if (!bnxt_ulp_registered(edev) && BNXT_NEW_RM(bp)) {
		...
		resv_msix = hw_resc->resv_irqs - bp->cp_nr_rings;
		ulp_msix = min_t(int, resv_msix, ulp_msix);
		bnxt_set_ulp_msix_num(bp, ulp_msix);

Take 8 ULP vectors, 32 L2 NQs and a FW grant of resv_irqs = 34.
bnxt_get_num_msix() returns 40, and bnxt_change_msix(bp, 40) activates
entries 34-39 while rc stays 0.

bnxt_alloc_cp_rings() maps L2 NQ i to MSI-X index ulp_msix + i. That
puts L2 NQs 26-31 on entries FW never reserved, which is the
lost-completion case this patch is fixing.

The commit message limits this with "at least while no RoCE driver is
registered" and says the accounting predates the patch. The in-code
comment doesn't mention the RoCE case.

Could the sizing be bounded by hw_resc->resv_irqs here? Or could the
registered ULP vectors be counted against resv_irqs in
__bnxt_reserve_rings()?

>  		if (bnxt_change_msix(bp, irqs_required) != irqs_required)
>  			rc = -ENOSPC;
>  	}

[Severity: High]
This is a pre-existing issue, but can this branch call bnxt_change_msix()
while bp->irq_tbl is NULL?

bnxt_clear_int_mode() frees the table but leaves bp->total_irqs as it
is:

static void bnxt_clear_int_mode(struct bnxt *bp)
{
	pci_free_irq_vectors(bp->pdev);

	kfree(bp->irq_tbl);
	bp->irq_tbl = NULL;
}

It is called from bnxt_hwrm_if_change() on fw_reset or caps_change, just
before bnxt_cancel_reservations(). It is also called from
bnxt_io_slot_reset().

The next bnxt_reserve_rings(bp, true) call comes from __bnxt_open_nic()
or bnxt_io_resume(). At that point bnxt_need_reserve_rings() is true and
pci_msix_can_alloc_dyn() is still true. So irq_change is set whenever
irqs_required differs from the stale bp->total_irqs.

If the count passed to bnxt_change_msix() is below the stale
bp->total_irqs, the trim loop then runs through a NULL bp->irq_tbl:

		map.virq = bp->irq_tbl[i - 1].vector;
		pci_msix_free_irq(bp->pdev, map);
		bp->irq_tbl[i - 1].vector = 0;

This could already happen when the pre-reservation count was below the
stale total. The recompute after __bnxt_reserve_rings() adds a new
trigger: pre-reservation count > stale total_irqs > post-reservation
count.

Before this patch that case took the grow loop instead. There,
pci_msix_alloc_irq_at() failed cleanly and the result was -ENOSPC.

The new !bnxt_need_reserve_rings() branch above checks bp->irq_tbl.
Should this branch check it as well?

[ ... ]

> @@ -15093,6 +15113,7 @@ int bnxt_check_rings(struct bnxt *bp, int tx, int rx, bool sh, int tcs,
>  			hwr.cp = min_t(int, hwr.cp, bnxt_get_max_func_irqs(bp));
>  		}
>  		if (hwr.cp > bp->total_irqs) {
> +			int old_total = bp->total_irqs;
>  			int total_msix = bnxt_change_msix(bp, hwr.cp);
>  
>  			if (total_msix < hwr.cp) {
> @@ -15100,6 +15121,17 @@ int bnxt_check_rings(struct bnxt *bp, int tx, int rx, bool sh, int tcs,
>  					    hwr.cp, total_msix);
>  				rc = -ENOSPC;
>  			}
> +			/* FW has not reserved the new vectors yet, and writes to
> +			 * MSI-X table entries beyond the reserved IRQs don't
> +			 * stick (seen on BCM57508).  Free them again;
> +			 * bnxt_reserve_rings() allocates them after
> +			 * __bnxt_reserve_rings().  Without the new resource
> +			 * manager there is no IRQ reservation and
> +			 * bnxt_reserve_rings() does not grow the vectors, so
> +			 * keep them.
> +			 */
> +			if (BNXT_NEW_RM(bp))
> +				bnxt_change_msix(bp, old_total);

[Severity: Low]
With the vectors freed again here, a 0 return from bnxt_check_rings() no
longer means they will still be available at reopen. Callers such as
bnxt_set_channels() act on that result:

bnxt_set_channels()
  bnxt_check_rings()          <- allocates, then frees the vectors
  bnxt_close_nic()
  (rx/tx ring counts updated)
  bnxt_open_nic()
    bnxt_reserve_rings()
      __bnxt_reserve_rings()  <- FW reservation committed
      bnxt_change_msix()      <- can now fail with -ENOSPC

Suppose the second allocation fails, for example because IRQ descriptor
allocation fails. Would an ethtool -L request that was already accepted
leave the interface down with "ring reservation/IRQ init failure"?

Before this patch, that failure would have come back from
bnxt_check_rings() before the device was closed.

The commit message notes that the allocation can now fail after FW has
committed the reservation, and the next open retries it.

>  		}
>  	}
>  	return rc;

[Severity: Medium]
This isn't a bug introduced by this patch, but bnxt_check_rings() goes
through bnxt_hwrm_check_rings()->bnxt_hwrm_check_pf_rings(), which uses
the request without a NULL check:

	req = __bnxt_hwrm_reserve_pf_rings(bp, hwr);
	flags = FUNC_CFG_REQ_FLAGS_TX_ASSETS_TEST;
	...
	req->flags = cpu_to_le32(flags);

__bnxt_hwrm_reserve_pf_rings() returns NULL when
bnxt_hwrm_func_cfg_short_req_init() fails. That happens, for example,
when dma_pool_alloc() fails in __hwrm_req_init().

Can this dereference a NULL req under memory pressure?
bnxt_hwrm_check_vf_rings() appears to follow the same pattern.

-- 
Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261028114933.256298-1-vlad.wing%40gmail.com