linux-kernel - Re: [PATCH v3] PCI: hv: Return zero, not garbage, when reading PCI_INTERRUPT

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Message-ID: <ZoTZTvL-SKxZEmu5@liuwe-devbox-debian-v2>
Date: Wed, 3 Jul 2024 04:53:34 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Linux on Hyper-V List <linux-hyperv@...r.kernel.org>
Cc: Wei Liu <wei.liu@...nel.org>, stable@...nel.org,
	Michael Kelley <mhklinux@...look.com>,
	"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 v3] PCI: hv: Return zero, not garbage, when reading
 PCI_INTERRUPT_PIN

On Mon, Jul 01, 2024 at 08:26:05PM +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. Garbage is returned in that 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>
> Reviewed-by: Michael Kelley <mhklinux@...look.com>

Bjorn & other PCI maintainers, do you want to pick this up via your
tree?

I can pick this up via the hyperv tree if you prefer.

Thanks,
Wei.

> ---
> v3:
> * Change commit subject line and message per Bjorn's suggestion
> 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
>