Commit 87c01d57 authored by Alistair Popple's avatar Alistair Popple Committed by Linus Torvalds
Browse files

mm/hmm.c: allow VM_MIXEDMAP to work with hmm_range_fault 

hmm_range_fault() can be used instead of get_user_pages() for devices
which allow faulting however unlike get_user_pages() it will return an
error when used on a VM_MIXEDMAP range.

To make hmm_range_fault() more closely match get_user_pages() remove
this restriction.  This requires dealing with the !ARCH_HAS_PTE_SPECIAL
case in hmm_vma_handle_pte().  Rather than replicating the logic of
vm_normal_page() call it directly and do a check for the zero pfn
similar to what get_user_pages() currently does.

Also add a test to hmm selftest to verify functionality.

Link: https://lkml.kernel.org/r/20211104012001.2555676-1-apopple@nvidia.com


Fixes: da4c3c73 ("mm/hmm/mirror: helper to snapshot CPU page table")
Signed-off-by: default avatarAlistair Popple <apopple@nvidia.com>
Reviewed-by: default avatarJason Gunthorpe <jgg@nvidia.com>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent cab0a7c1

lib/test_hmm.c

+24 −0
Original line number Diff line number Diff line
@@ -1086,9 +1086,33 @@ static long dmirror_fops_unlocked_ioctl(struct file *filp, 
	return 0;

}



static int dmirror_fops_mmap(struct file *file, struct vm_area_struct *vma)

{

	unsigned long addr;



	for (addr = vma->vm_start; addr < vma->vm_end; addr += PAGE_SIZE) {

		struct page *page;

		int ret;



		page = alloc_page(GFP_KERNEL | __GFP_ZERO);

		if (!page)

			return -ENOMEM;



		ret = vm_insert_page(vma, addr, page);

		if (ret) {

			__free_page(page);

			return ret;

		}

		put_page(page);

	}



	return 0;

}



static const struct file_operations dmirror_fops = {

	.open		= dmirror_fops_open,

	.release	= dmirror_fops_release,

	.mmap		= dmirror_fops_mmap,

	.unlocked_ioctl = dmirror_fops_unlocked_ioctl,

	.llseek		= default_llseek,

	.owner		= THIS_MODULE,

mm/hmm.c

+3 −2
Original line number Diff line number Diff line
@@ -300,7 +300,8 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, 
	 * Since each architecture defines a struct page for the zero page, just

	 * fall through and treat it like a normal page.

	 */

	if (pte_special(pte) && !pte_devmap(pte) &&

	if (!vm_normal_page(walk->vma, addr, pte) &&

	    !pte_devmap(pte) &&

	    !is_zero_pfn(pte_pfn(pte))) {

		if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) {

			pte_unmap(ptep);
@@ -518,7 +519,7 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end, 
	struct hmm_range *range = hmm_vma_walk->range;

	struct vm_area_struct *vma = walk->vma;



	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP | VM_MIXEDMAP)) &&

	if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)) &&

	    vma->vm_flags & VM_READ)

		return 0;

tools/testing/selftests/vm/hmm-tests.c

+42 −0
Original line number Diff line number Diff line
@@ -1248,6 +1248,48 @@ TEST_F(hmm, anon_teardown) 
	}

}



/*

 * Test memory snapshot without faulting in pages accessed by the device.

 */

TEST_F(hmm, mixedmap)

{

	struct hmm_buffer *buffer;

	unsigned long npages;

	unsigned long size;

	unsigned char *m;

	int ret;



	npages = 1;

	size = npages << self->page_shift;



	buffer = malloc(sizeof(*buffer));

	ASSERT_NE(buffer, NULL);



	buffer->fd = -1;

	buffer->size = size;

	buffer->mirror = malloc(npages);

	ASSERT_NE(buffer->mirror, NULL);





	/* Reserve a range of addresses. */

	buffer->ptr = mmap(NULL, size,

			   PROT_READ | PROT_WRITE,

			   MAP_PRIVATE,

			   self->fd, 0);

	ASSERT_NE(buffer->ptr, MAP_FAILED);



	/* Simulate a device snapshotting CPU pagetables. */

	ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_SNAPSHOT, buffer, npages);

	ASSERT_EQ(ret, 0);

	ASSERT_EQ(buffer->cpages, npages);



	/* Check what the device saw. */

	m = buffer->mirror;

	ASSERT_EQ(m[0], HMM_DMIRROR_PROT_READ);



	hmm_buffer_free(buffer);

}



/*

 * Test memory snapshot without faulting in pages accessed by the device.

 */