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

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Date: Wed, 26 Jun 2024 10:10:39 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Wei Liu <wei.liu@...nel.org>
Cc: 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

1) Capitalize subject to match history
2) Say something more specific than "fix reading ..."

Apparently this returns garbage in some case where you want to return
zero?

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
>