Re: [PATCH v6 13/25] iommufd: Add mmap interface

[Nicolin Chen]

On Mon, Jun 16, 2025 at 11:13:19AM -0300, Jason Gunthorpe wrote:
> On Sat, Jun 14, 2025 at 12:14:38AM -0700, Nicolin Chen wrote:
> 
> > +/* Entry for iommufd_ctx::mt_mmap */
> > +struct iommufd_mmap {
> > +   struct iommufd_object *owner;
> > +
> > +   /* Allocated start position in mt_mmap tree */
> > +   unsigned long startp;
> 
> pgoff_t, looks like this is already in PAGE_SIZE units.
> 
> > +   /* Physical range for io_remap_pfn_range() */
> > +   unsigned long mmio_pfn;
> 
> physaddr_t and maybe don't use pfn?
> 
> > +   unsigned long num_pfns;
> 
> size_t

I made the following changes, though I kept "unsigned long" for
"vm_pgoff" aligning with vma->vm_pgoff:

diff --git a/drivers/iommu/iommufd/driver.c b/drivers/iommu/iommufd/driver.c
index d797b77e878c6..73fcf3a89bf82 100644
--- a/drivers/iommu/iommufd/driver.c
+++ b/drivers/iommu/iommufd/driver.c
@@ -53,19 +53,19 @@ int _iommufd_alloc_mmap(struct iommufd_ctx *ictx, struct 
iommufd_object *owner,
        if (!immap)
                return -ENOMEM;
        immap->owner = owner;
-       immap->num_pfns = length >> PAGE_SHIFT;
-       immap->mmio_pfn = mmio_addr >> PAGE_SHIFT;
+       immap->length = length;
+       immap->mmio_addr = mmio_addr;
 
-       rc = mtree_alloc_range(&ictx->mt_mmap, &startp, immap, immap->num_pfns,
-                              0, U32_MAX >> PAGE_SHIFT, GFP_KERNEL);
+       rc = mtree_alloc_range(&ictx->mt_mmap, &startp, immap, immap->length,
+                              0, PHYS_ADDR_MAX, GFP_KERNEL);
        if (rc < 0) {
                kfree(immap);
                return rc;
        }
 
-       immap->startp = startp;
-       /* mmap() syscall will right-shift the offset in vma->vm_pgoff */
-       *offset = startp << PAGE_SHIFT;
+       /* mmap() syscall will right-shift the offset in vma->vm_pgoff too */
+       immap->vm_pgoff = startp >> PAGE_SHIFT;
+       *offset = startp;
        return 0;
 }
 EXPORT_SYMBOL_NS_GPL(_iommufd_alloc_mmap, "IOMMUFD");
diff --git a/drivers/iommu/iommufd/iommufd_private.h 
b/drivers/iommu/iommufd/iommufd_private.h
index cc9088ba5c812..ebac6a4b3538c 100644
--- a/drivers/iommu/iommufd/iommufd_private.h
+++ b/drivers/iommu/iommufd/iommufd_private.h
@@ -61,12 +61,12 @@ struct iommufd_ctx {
 struct iommufd_mmap {
        struct iommufd_object *owner;
 
-       /* Allocated start position in mt_mmap tree */
-       unsigned long startp;
+       /* Page-shifted start position in mt_mmap to validate vma->vm_pgoff */
+       unsigned long vm_pgoff;
 
        /* Physical range for io_remap_pfn_range() */
-       unsigned long mmio_pfn;
-       unsigned long num_pfns;
+       phys_addr_t mmio_addr;
+       size_t length;
 };
 
 /*
diff --git a/drivers/iommu/iommufd/main.c b/drivers/iommu/iommufd/main.c
index 339a269ebbc81..0fb81a905cb13 100644
--- a/drivers/iommu/iommufd/main.c
+++ b/drivers/iommu/iommufd/main.c
@@ -514,17 +514,15 @@ static int iommufd_fops_mmap(struct file *filp, struct 
vm_area_struct *vma)
        if (vma->vm_flags & VM_EXEC)
                return -EPERM;
 
-       /* vma->vm_pgoff carries an index to an mtree entry (immap) */
-       immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff);
+       /* vma->vm_pgoff carries a page-shifted start position to an immap */
+       immap = mtree_load(&ictx->mt_mmap, vma->vm_pgoff << PAGE_SHIFT);
        if (!immap)
                return -ENXIO;
        /*
-        * mtree_load() returns the immap for any contained pgoff, only allow
-        * the immap thing to be mapped
+        * mtree_load() returns the immap for any contained mmio_addr, so only
+        * allow the exact immap thing to be mapped
         */
-       if (vma->vm_pgoff != immap->startp)
-               return -ENXIO;
-       if (length != immap->num_pfns << PAGE_SHIFT)
+       if (vma->vm_pgoff != immap->vm_pgoff || length != immap->length)
                return -ENXIO;
 
        vma->vm_pgoff = 0;
@@ -532,7 +530,8 @@ static int iommufd_fops_mmap(struct file *filp, struct 
vm_area_struct *vma)
        vma->vm_ops = &iommufd_vma_ops;
        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 
-       rc = io_remap_pfn_range(vma, vma->vm_start, immap->mmio_pfn, length,
+       rc = io_remap_pfn_range(vma, vma->vm_start,
+                               immap->mmio_addr >> PAGE_SHIFT, length,
                                vma->vm_page_prot);
        if (rc)
                return rc;