linux-kernel - Re: [PATCH v3 2/2] iommu/arm-smmu-v3: Replace vsmmu_size/type with get_viommu

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Message-ID: <aINL66r_1NO3Nx-f@google.com>
Date: Fri, 25 Jul 2025 09:18:35 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: Pranjal Shrivastava <praan@...gle.com>, jgg@...dia.com, will@...nel.org,
	joro@...tes.org, robin.murphy@....com,
	linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 2/2] iommu/arm-smmu-v3: Replace vsmmu_size/type with
 get_viommu_size

Hi Nicolin,

On Thu, Jul 24, 2025 at 02:49:28PM -0700, Nicolin Chen wrote:
> On Thu, Jul 24, 2025 at 08:55:50PM +0000, Pranjal Shrivastava wrote:
> > On Wed, Jul 23, 2025 at 06:58:20PM +0000, Pranjal Shrivastava wrote:
> > > On Wed, Jul 23, 2025 at 11:05:26AM -0700, Nicolin Chen wrote:
> > > > On Wed, Jul 23, 2025 at 01:37:53PM +0000, Pranjal Shrivastava wrote:
> > > > > On Mon, Jul 21, 2025 at 01:04:44PM -0700, Nicolin Chen wrote:
> > > > > > @@ -1273,6 +1279,10 @@ tegra241_cmdqv_init_vintf_user(struct arm_vsmmu *vsmmu,
> > > > > >  	phys_addr_t page0_base;
> > > > > >  	int ret;
> > > > > >  
> > > > > > +	/* Unsupported type was rejected in tegra241_cmdqv_get_vintf_size() */
> > 
> > Sorry, if this wasn't clear in the previous comment. I meant this
> > comment must be updated, the "unsupported type" wasn't rejected in
> > vintf_size, rather the type got corrupted which brought us here.
> 
> Any unsupported type would be indeed rejected by the init op
> callback. There is nothing wrong with that statement.
> 
> It indicates that we shouldn't see an unsupported type here,
> unless some serious kernel bug like data corruption happens,
> which is implied by the WARN_ON itself.
> 
> > Had the
> > vintf_size rejected it, we wouldn't be calling the init op.
> 
> A data corruption could happen any time, not related to the
> init op. A concurrent buggy thread can overwrite the vIOMMU
> object when a write access to its adjacent memory overflows.

Can you please elaborate on that, as memory corruption can happen
any time event after the next check and there is no way to defend
against that?

Thanks,
Mostafa

> 
> Nicolin