On 27 October 2021 09:13:36 BST, Josef Johansson <josef@xxxxxxxxxxx> wrote: >On 10/27/21 08:24, David Woodhouse wrote: >> On Mon, 2021-10-25 at 21:21 +0200, Josef Johansson wrote: >>> + if (!(pci_msi_ignore_mask || entry->msi_attrib.is_virtual)) >> Is it just me, or is that a lot easier to read if you write it as the >> tautologically-identical (!pci_msi_ignore_mask && !entry->…is_virtual)? >Sure, the less parentheses the better. >> >>> @@ -546,7 +548,8 @@ static int msi_capability_init(struct pci_dev *dev, int nvec, >>> return -ENOMEM; >>> /* All MSIs are unmasked by default; mask them all * >>> - pci_msi_mask(entry, msi_multi_mask(entry)) >>> + if (!pci_msi_ignore_mask) >>> + pci_msi_mask(entry, msi_multi_mask(entry)); >>> >>> list_add_tail(&entry->list, dev_to_msi_list(&dev->dev)); >> >> Hm, I thought that older kernels *did* do this part (or at least the >> later ones in pci_msi*_hutdown). I was watching it when I did the Xen >> hosting implementation I mentioned before; even a hack to unmask them >> all when the VM was started, wasn't working because the guest would >> *mask* all MSI-X, just never unmask them again. >When you're saying *did* here, do you mean that they mask even though >pci_msi_ignore_mask = 0? > >As I was looking through pre Thomas' changes and post, it seems that we >did indeed >check for pci_msi_ignore_mask in msi_capability_init. Ah, maybe not so old. When my VMM part didn't work with standard ancient distro test images I turned to a relatively current git HEAD. So I was probably just unfortunate, and masking MSI under Xen at setup time was a temporary aberration; on older kernels the hack of enabling each vector at startup might have worked? I'll disable my eventual VMM-side fix and retest different guest kernels to be sure (and to make sure I have the full permutation set for regression testing because regardless of how insane Xen's behaviour is, I need to faithfully emulate it for every Linux kernel behaviour that existed). -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
