linux-kernel - Re: [PATCH v4 05/23] iommufd/driver: Let iommufd_viommu

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Message-ID: <aCemeved47HE6Q2B@Asurada-Nvidia>
Date: Fri, 16 May 2025 13:56:26 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: <kevin.tian@...el.com>, <corbet@....net>, <will@...nel.org>,
	<bagasdotme@...il.com>, <robin.murphy@....com>, <joro@...tes.org>,
	<thierry.reding@...il.com>, <vdumpa@...dia.com>, <jonathanh@...dia.com>,
	<shuah@...nel.org>, <jsnitsel@...hat.com>, <nathan@...nel.org>,
	<peterz@...radead.org>, <yi.l.liu@...el.com>, <mshavit@...gle.com>,
	<praan@...gle.com>, <zhangzekun11@...wei.com>, <iommu@...ts.linux.dev>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-tegra@...r.kernel.org>,
	<linux-kselftest@...r.kernel.org>, <patches@...ts.linux.dev>,
	<mochs@...dia.com>, <alok.a.tiwari@...cle.com>, <vasant.hegde@....com>
Subject: Re: [PATCH v4 05/23] iommufd/driver: Let iommufd_viommu_alloc helper
 save ictx to viommu->ictx

On Fri, May 16, 2025 at 10:28:45AM -0300, Jason Gunthorpe wrote:
> On Thu, May 15, 2025 at 07:05:45PM -0700, Nicolin Chen wrote:
> 
> > Otherwise, they would be something like:
> > 	// in my_viommu_alloc()
> > 	my_viommu = iommufd_viommu_alloc(ucmd, ...);
> > 	iommufd_viommu_alloc_mmap(ucmd->ictx, my_viommu, ...);
> > 	iommufd_viommu_destroy_mmap(ucmd->ictx, my_viommu, ...);
> > 	// in my_viommu_destory()
> > 	iommufd_viommu_destroy_mmap(my_viommu->ictx, my_viommu ...);
> 
> Yes, this is how the other objects work..
> 
> > That being said, I ended up doing something more in this patch
> > for the ucmd rework and Kevin's comments:
> > 
> > diff --git a/drivers/iommu/iommufd/iommufd_private.h b/drivers/iommu/iommufd/iommufd_private.h
> > index 98fe5a49c9606..ddd144031af5d 100644
> > --- a/drivers/iommu/iommufd/iommufd_private.h
> > +++ b/drivers/iommu/iommufd/iommufd_private.h
> > @@ -136,14 +136,6 @@ int iopt_pin_pages(struct io_pagetable *iopt, unsigned long iova,
> >  void iopt_unpin_pages(struct io_pagetable *iopt, unsigned long iova,
> >  		      unsigned long length);
> >  
> > -struct iommufd_ucmd {
> > -	struct iommufd_ctx *ictx;
> > -	void __user *ubuffer;
> > -	u32 user_size;
> > -	void *cmd;
> > -	struct iommufd_object *alloced_obj;
> > -};
> 
> You don't need to move this unless you are using inlines. Just use a
> forward declaration.

Since we forward ucmd now, ictx is in the ucmd so we need this
structure for:

-		if (!IS_ERR(ret))                                              \
+		if (!IS_ERR(ret)) {                                            \
 			ret->member.ops = viommu_ops;                          \
+			ret->member.ictx = ucmd->ictx;                         \
+		}                                                              \

Or, we could have a smaller:

#define ucmd_to_ictx(ucmd) (struct iommufd_ctx *)(ucmd)

and add a line of comments in struct iommufd_ucmd:

 struct iommufd_ucmd {
-	struct iommufd_ctx *ictx;
+	struct iommufd_ctx *ictx; /* Do not move; must be the first member */
 	void __user *ubuffer;
 	u32 user_size;
 	void *cmd;
 	struct iommufd_object *alloced_obj;
 };

Thanks
Nicolin