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

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Message-ID: <ZoMLMJ9aIPs1lt8a@liuwe-devbox-debian-v2>
Date: Mon, 1 Jul 2024 20:01:52 +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 Mon, Jul 01, 2024 at 12:20:53PM -0500, Bjorn Helgaas wrote:
> On Mon, Jul 01, 2024 at 06:16:18AM +0000, Wei Liu wrote:
> > 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"?
> 
> Yes.  Look at the history:
> 
>   $ git log --oneline --no-merges drivers/pci/controller/pci-hyperv.c
>   b5ff74c1ef50 PCI: hv: Fix ring buffer size calculation
>   07e8f88568f5 x86/apic: Drop apic::delivery_mode
>   f741bcadfe52 PCI: hv: Annotate struct hv_dr_state with __counted_by
>   04bbe863241a PCI: hv: Fix a crash in hv_pci_restore_msi_msg() during hibernation
>   067d6ec7ed5b PCI: hv: Add a per-bus mutex state_lock
>   a847234e24d0 Revert "PCI: hv: Fix a timing issue which causes kdump to fail occasionally"
>   add9195e69c9 PCI: hv: Remove the useless hv_pcichild_state from struct hv_pci_dev
>   2738d5ab7929 PCI: hv: Fix a race condition in hv_irq_unmask() that can cause panic
>   ...
> 
> > > 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
> 
> Maybe:
> 
>   PCI: hv: Return zero, not garbage, when reading 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>
> 
> Looks fine.

Thanks. I will resend with the updated commit message.