Messages in this thread | ![/](/images/icornerl.gif) | | From | "Tian, Kevin" <> | Subject | RE: [PATCH 2/2] iommu/vt-d: Share DMAR fault IRQ to prevent vector exhaustion | Date | Tue, 9 Apr 2024 07:07:22 +0000 |
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> From: Jacob Pan <jacob.jun.pan@linux.intel.com> > Sent: Tuesday, April 9, 2024 1:39 AM > > Hi Jacob, > > On Mon, 8 Apr 2024 09:05:56 -0700, Jacob Pan > <jacob.jun.pan@linux.intel.com> wrote: > > > Hi Kevin, > > > > On Mon, 8 Apr 2024 08:48:54 +0000, "Tian, Kevin" <kevin.tian@intel.com> > > wrote: > > > > > > From: Jacob Pan <jacob.jun.pan@linux.intel.com> > > > > Sent: Thursday, April 4, 2024 7:46 AM > > > > > > > > @@ -1182,7 +1182,6 @@ static void free_iommu(struct intel_iommu > > > > *iommu) > > > > iommu->pr_irq = 0; > > > > } > > > > free_irq(iommu->fault_irq, iommu); > > > > - dmar_free_hwirq(iommu->fault_irq); > > > > > > You still want to free the vector for the iommu which first gets the > > > vector allocated. > > > > > I think we always want to keep this vector since the system always needs > > one vector to share. We will never offline all the IOMMUs, right?
Not about offline. Just about the common rule of cleaning up a resource when all of its users are destroyed.
> > > > + > > > > + /* > > > > + * Only the owner IOMMU of the shared IRQ has its fault event > > > > + * interrupt unmasked after request_irq(), the rest are > > > > explicitly > > > > + * unmasked. > > > > + */ > > > > + if (!(iommu->flags & VTD_FLAG_FAULT_IRQ_OWNER)) > > > > + dmar_fault_irq_unmask(iommu); > > > > + > > > > > > em there is a problem in dmar_msi_mask() and dmar_msi_mask() > > > which only touches the owner IOMMU. With this shared vector > > > approach we should mask/unmask all IOMMU's together. > > I thought about this as well, in addition to fault_irq, > > dmar_msi_mask/unmask() are used for other DMAR irqs, page request and > > perfmon. So we need a special case for fault_irq there, it is not pretty.
yes, that is the part which I don't really like.
> > > > I added a special case here in this patch, thinking we never mask the > > fault_irq since we need to cover the lifetime of the system. I have looked > > at: > > 1.IOMMU suspend/resume, no mask/unmask > Actually, we do call mask/unmask in suspend/unmask noirq phase. > And DMAR-MSI chip has IRQCHIP_SKIP_SET_WAKE flag. > > So you are right, I am missing this case where non-owner IOMMU's fault_irqs > are not masked/unmasked. >
and it's not good to code a mask/unmask callback upon fixed assumptions on when irq core may call mask/unmask as the latter part can change w/o noting the broken assumption in such callback.
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