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From: Wei Liu <wei.liu@kernel.org>
To: Praveen Kumar <kumarpraveen@linux.microsoft.com>
Cc: Wei Liu <wei.liu@kernel.org>,
	Linux on Hyper-V List <linux-hyperv@vger.kernel.org>,
	virtualization@lists.linux-foundation.org,
	Linux Kernel List <linux-kernel@vger.kernel.org>,
	Michael Kelley <mikelley@microsoft.com>,
	Vineeth Pillai <viremana@linux.microsoft.com>,
	Sunil Muthuswamy <sunilmut@microsoft.com>,
	Nuno Das Neves <nunodasneves@linux.microsoft.com>,
	pasha.tatashin@soleen.com, "K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Dexuan Cui <decui@microsoft.com>, Joerg Roedel <joro@8bytes.org>,
	Will Deacon <will@kernel.org>,
	"open list:IOMMU DRIVERS" <iommu@lists.linux-foundation.org>
Subject: Re: [RFC v1 6/8] mshv: command line option to skip devices in PV-IOMMU
Date: Tue, 3 Aug 2021 21:56:17 +0000	[thread overview]
Message-ID: <20210803215617.fzx2vrzhsabrrolc@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <4a6918ea-e3e5-55c9-a12d-bee7261301fd@linux.microsoft.com>

On Wed, Aug 04, 2021 at 12:20:42AM +0530, Praveen Kumar wrote:
> On 09-07-2021 17:13, Wei Liu wrote:
> > Some devices may have been claimed by the hypervisor already. One such
> > example is a user can assign a NIC for debugging purpose.
> > 
> > Ideally Linux should be able to tell retrieve that information, but
> > there is no way to do that yet. And designing that new mechanism is
> > going to take time.
> > 
> > Provide a command line option for skipping devices. This is a stopgap
> > solution, so it is intentionally undocumented. Hopefully we can retire
> > it in the future.
> > 
> > Signed-off-by: Wei Liu <wei.liu@kernel.org>
> > ---
> >  drivers/iommu/hyperv-iommu.c | 45 ++++++++++++++++++++++++++++++++++++
> >  1 file changed, 45 insertions(+)
> > 
> > diff --git a/drivers/iommu/hyperv-iommu.c b/drivers/iommu/hyperv-iommu.c
> > index 043dcff06511..353da5036387 100644
> > --- a/drivers/iommu/hyperv-iommu.c
> > +++ b/drivers/iommu/hyperv-iommu.c
> > @@ -349,6 +349,16 @@ static const struct irq_domain_ops hyperv_root_ir_domain_ops = {
> >  
> >  #ifdef CONFIG_HYPERV_ROOT_PVIOMMU
> >  
> > +/* The IOMMU will not claim these PCI devices. */
> > +static char *pci_devs_to_skip;
> > +static int __init mshv_iommu_setup_skip(char *str) {
> > +	pci_devs_to_skip = str;
> > +
> > +	return 0;
> > +}
> > +/* mshv_iommu_skip=(SSSS:BB:DD.F)(SSSS:BB:DD.F) */
> > +__setup("mshv_iommu_skip=", mshv_iommu_setup_skip);
> > +
> >  /* DMA remapping support */
> >  struct hv_iommu_domain {
> >  	struct iommu_domain domain;
> > @@ -774,6 +784,41 @@ static struct iommu_device *hv_iommu_probe_device(struct device *dev)
> >  	if (!dev_is_pci(dev))
> >  		return ERR_PTR(-ENODEV);
> >  
> > +	/*
> > +	 * Skip the PCI device specified in `pci_devs_to_skip`. This is a
> > +	 * temporary solution until we figure out a way to extract information
> > +	 * from the hypervisor what devices it is already using.
> > +	 */
> > +	if (pci_devs_to_skip && *pci_devs_to_skip) {
> > +		int pos = 0;
> > +		int parsed;
> > +		int segment, bus, slot, func;
> > +		struct pci_dev *pdev = to_pci_dev(dev);
> > +
> > +		do {
> > +			parsed = 0;
> > +
> > +			sscanf(pci_devs_to_skip + pos,
> > +				" (%x:%x:%x.%x) %n",
> > +				&segment, &bus, &slot, &func, &parsed);
> > +
> > +			if (parsed <= 0)
> > +				break;
> > +
> > +			if (pci_domain_nr(pdev->bus) == segment &&
> > +				pdev->bus->number == bus &&
> > +				PCI_SLOT(pdev->devfn) == slot &&
> > +				PCI_FUNC(pdev->devfn) == func)
> > +			{
> > +				dev_info(dev, "skipped by MSHV IOMMU\n");
> > +				return ERR_PTR(-ENODEV);
> > +			}
> > +
> > +			pos += parsed;
> > +
> > +		} while (pci_devs_to_skip[pos]);
> 
> Is there a possibility of pci_devs_to_skip + pos > sizeof(pci_devs_to_skip)
> and also a valid memory ?

pos should point to the last parsed position. If parsing fails pos does
not get updated and the code breaks out of the loop. If parsing is
success pos should point to either the start of next element of '\0'
(end of string). To me this is good enough.

> I would recommend to have a check of size as well before accessing the
> array content, just to be safer accessing any memory.
> 

What check do you have in mind?

Wei.

> > +	}
> > +
> >  	vdev = kzalloc(sizeof(*vdev), GFP_KERNEL);
> >  	if (!vdev)
> >  		return ERR_PTR(-ENOMEM);
> > 
> 
> Regards,
> 
> ~Praveen.

  reply	other threads:[~2021-08-03 21:56 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-09 11:43 [RFC v1 0/8] MSHV: add PV-IOMMU driver Wei Liu
2021-07-09 11:43 ` [RFC v1 1/8] x86/hyperv: export hv_build_pci_dev_id Wei Liu
2021-07-09 11:43 ` [RFC v1 2/8] asm-generic/hyperv: add device domain definitions Wei Liu
2021-07-09 11:43 ` [RFC v1 3/8] intel/vt-d: make DMAR table parsing code more flexible Wei Liu
2021-07-09 12:56   ` Robin Murphy
2021-07-09 13:42     ` Wei Liu
2021-07-09 11:43 ` [RFC v1 4/8] intel/vt-d: export intel_iommu_get_resv_regions Wei Liu
2021-07-09 14:17   ` Lu Baolu
2021-07-09 14:21     ` Wei Liu
2021-07-09 11:43 ` [RFC v1 5/8] mshv: add paravirtualized IOMMU support Wei Liu
2021-08-03 18:40   ` Praveen Kumar
2021-08-03 21:47     ` Wei Liu
2021-08-04  6:43       ` Praveen Kumar
2021-08-10 10:46         ` Wei Liu
2021-07-09 11:43 ` [RFC v1 6/8] mshv: command line option to skip devices in PV-IOMMU Wei Liu
2021-07-09 12:46   ` Robin Murphy
2021-07-09 13:34     ` Wei Liu
2021-08-03 18:50   ` Praveen Kumar
2021-08-03 21:56     ` Wei Liu [this message]
2021-08-04  7:03       ` Praveen Kumar
2021-08-10 10:04         ` Wei Liu
2021-07-09 11:43 ` [RFC v1 7/8] mshv: implement in-kernel device framework Wei Liu
2021-07-09 13:02   ` Matthew Wilcox
2021-07-09 13:50     ` Wei Liu
2021-07-09 15:32       ` Matthew Wilcox
2021-07-09 16:27         ` Wei Liu
2021-07-09 16:38           ` Matthew Wilcox
2021-07-09 19:14             ` Wei Liu
2021-07-09 19:48               ` Matthew Wilcox
2021-07-09 20:11                 ` Wei Liu
2021-08-03 19:12   ` Praveen Kumar
2021-08-03 22:04     ` Wei Liu
2021-07-09 11:43 ` [RFC v1 8/8] mshv: add vfio bridge device Wei Liu
2021-08-03 19:27   ` Praveen Kumar
2021-08-10 10:52     ` Wei Liu

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