linux-kernel - Re: [PATCH v2] PCI: hv: fix reading of PCI_INTERRUPT

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Date: Mon, 1 Jul 2024 06:16:18 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Wei Liu <wei.liu@...nel.org>,
	Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
	stable@...nel.org, "K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Jake Oshins <jakeo@...rosoft.com>,
	"open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS" <linux-pci@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: hv: fix reading of PCI_INTERRUPT_PIN

On Wed, Jun 26, 2024 at 10:10:39AM -0500, Bjorn Helgaas wrote:
> 1) Capitalize subject to match history

What do you mean here? I got the "PCI: hv: ..." format from recent
commits. "PCI" is capitalized. You want to to capitalize "fix"?

> 2) Say something more specific than "fix reading ..."
> 
> Apparently this returns garbage in some case where you want to return
> zero?

Yes. *val is not changed in the old code, so garbage is returned.

Here is the updated commit message. I can resend once you confirm you're
happy with it.

    PCI: hv: Fix reading of PCI_INTERRUPT_PIN

    The intent of the code snippet is to always return 0 for both
    PCI_INTERRUPT_LINE and PCI_INTERRUPT_PIN.

    The check misses PCI_INTERRUPT_PIN. This patch fixes that.

    This is discovered by this call in VFIO:

        pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);

    The old code does not set *val to 0 because it misses the check for
    PCI_INTERRUPT_PIN. Garbage is returned in this case.

    Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
    Cc: stable@...nel.org
    Signed-off-by: Wei Liu <wei.liu@...nel.org>

Thanks,
Wei.


> 
> On Fri, Jun 21, 2024 at 09:00:18PM +0000, Wei Liu wrote:
> > The intent of the code snippet is to always return 0 for both
> > PCI_INTERRUPT_LINE and PCI_INTERRUPT_PIN.
> > 
> > The check misses PCI_INTERRUPT_PIN. This patch fixes that.
> > 
> > This is discovered by this call in VFIO:
> > 
> >     pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);
> > 
> > The old code does not set *val to 0 because it misses the check for
> > PCI_INTERRUPT_PIN.
> > 
> > Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
> > Cc: stable@...nel.org
> > Signed-off-by: Wei Liu <wei.liu@...nel.org>
> > ---
> > v2:
> > * Change the commit subject line and message
> > * Change the code according to feedback
> > ---
> >  drivers/pci/controller/pci-hyperv.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index 5992280e8110..cdd5be16021d 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -1130,8 +1130,8 @@ static void _hv_pcifront_read_config(struct hv_pci_dev *hpdev, int where,
> >  		   PCI_CAPABILITY_LIST) {
> >  		/* ROM BARs are unimplemented */
> >  		*val = 0;
> > -	} else if (where >= PCI_INTERRUPT_LINE && where + size <=
> > -		   PCI_INTERRUPT_PIN) {
> > +	} else if ((where >= PCI_INTERRUPT_LINE && where + size <= PCI_INTERRUPT_PIN) ||
> > +		   (where >= PCI_INTERRUPT_PIN && where + size <= PCI_MIN_GNT)) {
> >  		/*
> >  		 * Interrupt Line and Interrupt PIN are hard-wired to zero
> >  		 * because this front-end only supports message-signaled
> > -- 
> > 2.43.0
> >