[PATCH v8 6/8] mm: Selftests for exclusive device memory

Alistair Popple
2021-04-07T09:00:56Z

Adds some selftests for exclusive device memory.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Acked-by: Jason Gunthorpe <jgg@nvidia.com>
Tested-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
---
lib/test_hmm.c | 124 +++++++++++++++++++
lib/test_hmm_uapi.h | 2 +
tools/testing/selftests/vm/hmm-tests.c | 158 +++++++++++++++++++++++++
3 files changed, 284 insertions(+)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 5c9f5a020c1d..305a9d9e2b4c 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -25,6 +25,7 @@
#include <linux/swapops.h>
#include <linux/sched/mm.h>
#include <linux/platform_device.h>
+#include <linux/rmap.h>

#include "test_hmm_uapi.h"

@@ -46,6 +47,7 @@ struct dmirror_bounce {
unsigned long cpages;
};

+#define DPT_XA_TAG_ATOMIC 1UL
#define DPT_XA_TAG_WRITE 3UL

/*
@@ -619,6 +621,54 @@ static void dmirror_migrate_alloc_and_copy(struct migrate_vma *args,
}
}

+static int dmirror_check_atomic(struct dmirror *dmirror, unsigned long start,
+ unsigned long end)
+{
+ unsigned long pfn;
+
+ for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++) {
+ void *entry;
+ struct page *page;
+
+ entry = xa_load(&dmirror->pt, pfn);
+ page = xa_untag_pointer(entry);
+ if (xa_pointer_tag(entry) == DPT_XA_TAG_ATOMIC)
+ return -EPERM;
+ }
+
+ return 0;
+}
+
+static int dmirror_atomic_map(unsigned long start, unsigned long end,
+ struct page **pages, struct dmirror *dmirror)
+{
+ unsigned long pfn, mapped = 0;
+ int i;
+
+ /* Map the migrated pages into the device's page tables. */
+ mutex_lock(&dmirror->mutex);
+
+ for (i = 0, pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++, i++) {
+ void *entry;
+
+ if (!pages[i])
+ continue;
+
+ entry = pages[i];
+ entry = xa_tag_pointer(entry, DPT_XA_TAG_ATOMIC);
+ entry = xa_store(&dmirror->pt, pfn, entry, GFP_ATOMIC);
+ if (xa_is_err(entry)) {
+ mutex_unlock(&dmirror->mutex);
+ return xa_err(entry);
+ }
+
+ mapped++;
+ }
+
+ mutex_unlock(&dmirror->mutex);
+ return mapped;
+}
+
static int dmirror_migrate_finalize_and_map(struct migrate_vma *args,
struct dmirror *dmirror)
{
@@ -661,6 +711,71 @@ static int dmirror_migrate_finalize_and_map(struct migrate_vma *args,
return 0;
}

+static int dmirror_exclusive(struct dmirror *dmirror,
+ struct hmm_dmirror_cmd *cmd)
+{
+ unsigned long start, end, addr;
+ unsigned long size = cmd->npages << PAGE_SHIFT;
+ struct mm_struct *mm = dmirror->notifier.mm;
+ struct page *pages[64];
+ struct dmirror_bounce bounce;
+ unsigned long next;
+ int ret;
+
+ start = cmd->addr;
+ end = start + size;
+ if (end < start)
+ return -EINVAL;
+
+ /* Since the mm is for the mirrored process, get a reference first. */
+ if (!mmget_not_zero(mm))
+ return -EINVAL;
+
+ mmap_read_lock(mm);
+ for (addr = start; addr < end; addr = next) {
+ int i, mapped;
+
+ if (end < addr + (ARRAY_SIZE(pages) << PAGE_SHIFT))
+ next = end;
+ else
+ next = addr + (ARRAY_SIZE(pages) << PAGE_SHIFT);
+
+ ret = make_device_exclusive_range(mm, addr, next, pages, NULL);
+ mapped = dmirror_atomic_map(addr, next, pages, dmirror);
+ for (i = 0; i < ret; i++) {
+ if (pages[i]) {
+ unlock_page(pages[i]);
+ put_page(pages[i]);
+ }
+ }
+
+ if (addr + (mapped << PAGE_SHIFT) < next) {
+ mmap_read_unlock(mm);
+ mmput(mm);
+ return -EBUSY;
+ }
+ }
+ mmap_read_unlock(mm);
+ mmput(mm);
+
+ /* Return the migrated data for verification. */
+ ret = dmirror_bounce_init(&bounce, start, size);
+ if (ret)
+ return ret;
+ mutex_lock(&dmirror->mutex);
+ ret = dmirror_do_read(dmirror, start, end, &bounce);
+ mutex_unlock(&dmirror->mutex);
+ if (ret == 0) {
+ if (copy_to_user(u64_to_user_ptr(cmd->ptr), bounce.ptr,
+ bounce.size))
+ ret = -EFAULT;
+ }
+
+ cmd->cpages = bounce.cpages;
+ dmirror_bounce_fini(&bounce);
+ return ret;
+}
+
static int dmirror_migrate(struct dmirror *dmirror,
struct hmm_dmirror_cmd *cmd)
{
@@ -949,6 +1064,15 @@ static long dmirror_fops_unlocked_ioctl(struct file *filp,
ret = dmirror_migrate(dmirror, &cmd);
break;

+ case HMM_DMIRROR_EXCLUSIVE:
+ ret = dmirror_exclusive(dmirror, &cmd);
+ break;
+
+ case HMM_DMIRROR_CHECK_EXCLUSIVE:
+ ret = dmirror_check_atomic(dmirror, cmd.addr,
+ cmd.addr + (cmd.npages << PAGE_SHIFT));
+ break;
+
case HMM_DMIRROR_SNAPSHOT:
ret = dmirror_snapshot(dmirror, &cmd);
break;
diff --git a/lib/test_hmm_uapi.h b/lib/test_hmm_uapi.h
index 670b4ef2a5b6..f14dea5dcd06 100644
--- a/lib/test_hmm_uapi.h
+++ b/lib/test_hmm_uapi.h
@@ -33,6 +33,8 @@ struct hmm_dmirror_cmd {
#define HMM_DMIRROR_WRITE _IOWR('H', 0x01, struct hmm_dmirror_cmd)
#define HMM_DMIRROR_MIGRATE _IOWR('H', 0x02, struct hmm_dmirror_cmd)
#define HMM_DMIRROR_SNAPSHOT _IOWR('H', 0x03, struct hmm_dmirror_cmd)
+#define HMM_DMIRROR_EXCLUSIVE _IOWR('H', 0x04, struct hmm_dmirror_cmd)
+#define HMM_DMIRROR_CHECK_EXCLUSIVE _IOWR('H', 0x05, struct hmm_dmirror_cmd)

/*
* Values returned in hmm_dmirror_cmd.ptr for HMM_DMIRROR_SNAPSHOT.
diff --git a/tools/testing/selftests/vm/hmm-tests.c b/tools/testing/selftests/vm/hmm-tests.c
index 5d1ac691b9f4..864f126ffd78 100644
--- a/tools/testing/selftests/vm/hmm-tests.c
+++ b/tools/testing/selftests/vm/hmm-tests.c
@@ -1485,4 +1485,162 @@ TEST_F(hmm2, double_map)
hmm_buffer_free(buffer);
}

+/*
+ * Basic check of exclusive faulting.
+ */
+TEST_F(hmm, exclusive)
+{
+ struct hmm_buffer *buffer;
+ unsigned long npages;
+ unsigned long size;
+ unsigned long i;
+ int *ptr;
+ int ret;
+
+ npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+ ASSERT_NE(npages, 0);
+ size = npages << self->page_shift;
+
+ buffer = malloc(sizeof(*buffer));
+ ASSERT_NE(buffer, NULL);
+
+ buffer->fd = -1;
+ buffer->size = size;
+ buffer->mirror = malloc(size);
+ ASSERT_NE(buffer->mirror, NULL);
+
+ buffer->ptr = mmap(NULL, size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS,
+ buffer->fd, 0);
+ ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+ /* Initialize buffer in system memory. */
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ptr[i] = i;
+
+ /* Map memory exclusively for device access. */
+ ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_EXCLUSIVE, buffer, npages);
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(buffer->cpages, npages);
+
+ /* Check what the device read. */
+ for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i], i);
+
+ /* Fault pages back to system memory and check them. */
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i]++, i);
+
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i], i+1);
+
+ /* Check atomic access revoked */
+ ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_CHECK_EXCLUSIVE, buffer, npages);
+ ASSERT_EQ(ret, 0);
+
+ hmm_buffer_free(buffer);
+}
+
+TEST_F(hmm, exclusive_mprotect)
+{
+ struct hmm_buffer *buffer;
+ unsigned long npages;
+ unsigned long size;
+ unsigned long i;
+ int *ptr;
+ int ret;
+
+ npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+ ASSERT_NE(npages, 0);
+ size = npages << self->page_shift;
+
+ buffer = malloc(sizeof(*buffer));
+ ASSERT_NE(buffer, NULL);
+
+ buffer->fd = -1;
+ buffer->size = size;
+ buffer->mirror = malloc(size);
+ ASSERT_NE(buffer->mirror, NULL);
+
+ buffer->ptr = mmap(NULL, size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS,
+ buffer->fd, 0);
+ ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+ /* Initialize buffer in system memory. */
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ptr[i] = i;
+
+ /* Map memory exclusively for device access. */
+ ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_EXCLUSIVE, buffer, npages);
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(buffer->cpages, npages);
+
+ /* Check what the device read. */
+ for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i], i);
+
+ ret = mprotect(buffer->ptr, size, PROT_READ);
+ ASSERT_EQ(ret, 0);
+
+ /* Simulate a device writing system memory. */
+ ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_WRITE, buffer, npages);
+ ASSERT_EQ(ret, -EPERM);
+
+ hmm_buffer_free(buffer);
+}
+
+/*
+ * Check copy-on-write works.
+ */
+TEST_F(hmm, exclusive_cow)
+{
+ struct hmm_buffer *buffer;
+ unsigned long npages;
+ unsigned long size;
+ unsigned long i;
+ int *ptr;
+ int ret;
+
+ npages = ALIGN(HMM_BUFFER_SIZE, self->page_size) >> self->page_shift;
+ ASSERT_NE(npages, 0);
+ size = npages << self->page_shift;
+
+ buffer = malloc(sizeof(*buffer));
+ ASSERT_NE(buffer, NULL);
+
+ buffer->fd = -1;
+ buffer->size = size;
+ buffer->mirror = malloc(size);
+ ASSERT_NE(buffer->mirror, NULL);
+
+ buffer->ptr = mmap(NULL, size,
+ PROT_READ | PROT_WRITE,
+ MAP_PRIVATE | MAP_ANONYMOUS,
+ buffer->fd, 0);
+ ASSERT_NE(buffer->ptr, MAP_FAILED);
+
+ /* Initialize buffer in system memory. */
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ptr[i] = i;
+
+ /* Map memory exclusively for device access. */
+ ret = hmm_dmirror_cmd(self->fd, HMM_DMIRROR_EXCLUSIVE, buffer, npages);
+ ASSERT_EQ(ret, 0);
+ ASSERT_EQ(buffer->cpages, npages);
+
+ fork();
+
+ /* Fault pages back to system memory and check them. */
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i]++, i);
+
+ for (i = 0, ptr = buffer->ptr; i < size / sizeof(*ptr); ++i)
+ ASSERT_EQ(ptr[i], i+1);
+
+ hmm_buffer_free(buffer);
+}
+
TEST_HARNESS_MAIN
--
2.20.1