From: [email protected] <[email protected]> Sent: Sunday, September 13, 2026 4:23 PM >
In the patch Subject, capitalize "Hardwire" for historical consistency. See [1]. > Hyper-V Discrete Device Assignment (DDA) does not support legacy (INTX) > interrupts. When PCI_INTERRUPT_PIN is read, the pci-hyperv controller, > which captures configuration space accesses, returns 0 to the caller. > > However, the current code only captures 8bit read access, thus 16bit/32bit > are missed, forwarded to the host/HW, and may yield a non zero value. > > This fix addresses this issue, and makes sure that PCI_INTERRUPT_PIN is > hardwired to 0, while the other bytes, are those returned by the host/HW. It took me a bit to figure out what the above two paragraphs mean. For more precision, how about: The current code recognizes PCI_INTERRUPT_PIN reads and forces a zero value, but only for 8 bit reads. If a 16 or 32 bit read overlaps the field, it may be returned as a non-zero value. Fix this by recognizing such overlap, and forcing the PCI_INTERRUPT_PIN byte to zero while retaining the adjacent bytes returned by the host/HW. > > Signed-off-by: Asher Kariv <[email protected]> > Signed-off-by: Mukesh R <[email protected]> > Signed-off-by: Wei Liu <[email protected]> > --- > I found this in our internal tree, massaged the code and commit message, > and posted it. > > v2: fix a compilation error > --- > drivers/pci/controller/pci-hyperv.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/drivers/pci/controller/pci-hyperv.c > b/drivers/pci/controller/pci-hyperv.c > index 89816a2bd7cd..bb4e6ca4ac1c 100644 > --- a/drivers/pci/controller/pci-hyperv.c > +++ b/drivers/pci/controller/pci-hyperv.c > @@ -1240,6 +1240,16 @@ static void _hv_pcifront_read_config(struct hv_pci_dev > *hpdev, int where, > mb(); > } > spin_unlock_irqrestore(&hbus->config_lock, flags); > + > + /* > + * Make sure PCI_INTERRUPT_PIN is hard-wired to 0, since it > + * may be read using a 32bit read, which is skipped by the "may be included in a 16 bit or 32 bit read, which is skipped by the" > + * above emulation. > + */ > + if (where <= PCI_INTERRUPT_PIN && > + PCI_INTERRUPT_PIN < (where + size)) > + *((char *)val + PCI_INTERRUPT_PIN - where) = 0; > + Does this same handling need to be applied to PCI_INTERRUPT_LINE? > } else { > dev_err(dev, "Attempt to read beyond a function's config > space.\n"); > } Michael [1] https://lore.kernel.org/linux-hyperv/20240701172053.GA10100@bhelgaas/
