This handle page fault on behalf of device driver, unlike handle_mm_fault()
it does not trigger migration back to system memory for device memory.
Signed-off-by: Jérôme Glisse <jglisse@xxxxxxxxxx>
Signed-off-by: Evgeny Baskakov <ebaskakov@xxxxxxxxxx>
Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Mark Hairgrove <mhairgrove@xxxxxxxxxx>
Signed-off-by: Sherry Cheung <SCheung@xxxxxxxxxx>
Signed-off-by: Subhash Gutti <sgutti@xxxxxxxxxx>
---
include/linux/hmm.h | 26 +++++
mm/hmm.c | 269 ++++++++++++++++++++++++++++++++++++++++++++++------
2 files changed, 267 insertions(+), 28 deletions(-)
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index b5eafdc..f19c2a0 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -288,6 +288,32 @@ int hmm_vma_get_pfns(struct vm_area_struct *vma,
unsigned long end,
hmm_pfn_t *pfns);
bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range);
+
+
+/*
+ * Fault memory on behalf of device driver unlike handle_mm_fault() it will not
+ * migrate any device memory back to system memory. The hmm_pfn_t array will be
+ * updated with fault result and current snapshot of the CPU page table for the
+ * range.
+ *
+ * The mmap_sem must be taken in read mode before entering and it might be drop
+ * by the function if block argument is false, when that happen the function
+ * returns -EAGAIN.
+ *
+ * Return value does not reflect if the fault was successfull for every single
+ * address or not, you need to inspect the hmm_pfn_t array to determine fault
+ * status for that address. Trying to fault inside an invalid vma will result
+ * in -EINVAL.
+ *
+ * See function description in mm/hmm.c for documentation.
+ */
+int hmm_vma_fault(struct vm_area_struct *vma,
+ struct hmm_range *range,
+ unsigned long start,
+ unsigned long end,
+ hmm_pfn_t *pfns,
+ bool write,
+ bool block);
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
diff --git a/mm/hmm.c b/mm/hmm.c
index 0ef06df..a397d45 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -288,6 +288,15 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror)
}
EXPORT_SYMBOL(hmm_mirror_unregister);
+
+static void hmm_pfns_error(hmm_pfn_t *pfns,
+ unsigned long addr,
+ unsigned long end)
+{
+ for (; addr < end; addr += PAGE_SIZE, pfns++)
+ *pfns = HMM_PFN_ERROR;
+}
+
static void hmm_pfns_empty(hmm_pfn_t *pfns,
unsigned long addr,
unsigned long end)
@@ -304,10 +313,43 @@ static void hmm_pfns_special(hmm_pfn_t *pfns,
*pfns = HMM_PFN_SPECIAL;
}
-static void hmm_vma_walk(struct vm_area_struct *vma,
- unsigned long start,
- unsigned long end,
- hmm_pfn_t *pfns)
+static void hmm_pfns_clear(hmm_pfn_t *pfns,
+ unsigned long addr,
+ unsigned long end)
+{
+ unsigned long npfns = (end - addr) >> PAGE_SHIFT;
+
+ memset(pfns, 0, sizeof(*pfns) * npfns);
+}
+
+static int hmm_vma_do_fault(struct vm_area_struct *vma,
+ const hmm_pfn_t fault,
+ unsigned long addr,
+ hmm_pfn_t *pfn,
+ bool block)
+{
+ unsigned flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_REMOTE;
+ int r;
+
+ flags |= block ? 0 : FAULT_FLAG_ALLOW_RETRY;
+ flags |= (fault & HMM_PFN_WRITE) ? FAULT_FLAG_WRITE : 0;
+ r = handle_mm_fault(vma, addr, flags);
+ if (r & VM_FAULT_RETRY)
+ return -EAGAIN;
+ if (r & VM_FAULT_ERROR) {
+ *pfn = HMM_PFN_ERROR;
+ return -EFAULT;
+ }
+
+ return 0;
+}
+
+static int hmm_vma_walk(struct vm_area_struct *vma,
+ const hmm_pfn_t fault,
+ unsigned long start,
+ unsigned long end,
+ hmm_pfn_t *pfns,
+ bool block)
{
unsigned long addr, next;
hmm_pfn_t flag;
@@ -321,6 +363,7 @@ static void hmm_vma_walk(struct vm_area_struct *vma,
pmd_t *pmdp;
pte_t *ptep;
pmd_t pmd;
+ int ret;
/*
* We are accessing/faulting for a device from an unknown
@@ -331,15 +374,37 @@ static void hmm_vma_walk(struct vm_area_struct *vma,
next = pgd_addr_end(addr, end);
pgdp = pgd_offset(vma->vm_mm, addr);
if (pgd_none(*pgdp) || pgd_bad(*pgdp)) {
- hmm_pfns_empty(&pfns[i], addr, next);
- continue;
+ if (!(vma->vm_flags & VM_READ)) {
+ hmm_pfns_empty(&pfns[i], addr, next);
+ continue;
+ }
+ if (!fault) {
+ hmm_pfns_empty(&pfns[i], addr, next);
+ continue;
+ }
+ pudp = pud_alloc(vma->vm_mm, pgdp, addr);
+ if (!pudp) {
+ hmm_pfns_error(&pfns[i], addr, next);
+ continue;
+ }
}
next = pud_addr_end(addr, end);
pudp = pud_offset(pgdp, addr);
if (pud_none(*pudp) || pud_bad(*pudp)) {
- hmm_pfns_empty(&pfns[i], addr, next);
- continue;
+ if (!(vma->vm_flags & VM_READ)) {
+ hmm_pfns_empty(&pfns[i], addr, next);
+ continue;
+ }
+ if (!fault) {
+ hmm_pfns_empty(&pfns[i], addr, next);
+ continue;
+ }
+ pmdp = pmd_alloc(vma->vm_mm, pudp, addr);
+ if (!pmdp) {
+ hmm_pfns_error(&pfns[i], addr, next);
+ continue;
+ }
}
next = pmd_addr_end(addr, end);
@@ -347,8 +412,24 @@ static void hmm_vma_walk(struct vm_area_struct *vma,
pmd = pmd_read_atomic(pmdp);
barrier();
if (pmd_none(pmd) || pmd_bad(pmd)) {
- hmm_pfns_empty(&pfns[i], addr, next);
- continue;
+ if (!(vma->vm_flags & VM_READ)) {
+ hmm_pfns_empty(&pfns[i], addr, next);
+ continue;
+ }
+ if (!fault) {
+ hmm_pfns_empty(&pfns[i], addr, next);
+ continue;
+ }
+ /*
+ * Use pte_alloc() instead of pte_alloc_map, because we
+ * can't run pte_offset_map on the pmd, if an huge pmd
+ * could materialize from under us.
+ */
+ if (unlikely(pte_alloc(vma->vm_mm, pmdp, addr))) {
+ hmm_pfns_error(&pfns[i], addr, next);
+ continue;
+ }
+ pmd = *pmdp;
}
if (pmd_trans_huge(pmd) || pmd_devmap(pmd)) {
unsigned long pfn = pmd_pfn(pmd) + pte_index(addr);
@@ -356,10 +437,14 @@ static void hmm_vma_walk(struct vm_area_struct *vma,
if (pmd_protnone(pmd)) {
hmm_pfns_clear(&pfns[i], addr, next);
+ if (fault)
+ goto fault;
continue;
}
flags |= pmd_write(*pmdp) ? HMM_PFN_WRITE : 0;
flags |= pmd_devmap(pmd) ? HMM_PFN_DEVICE : 0;
+ if ((flags & fault) != fault)
+ goto fault;
for (; addr < next; addr += PAGE_SIZE, i++, pfn++)
pfns[i] = hmm_pfn_from_pfn(pfn) | flags;
continue;
@@ -370,41 +455,63 @@ static void hmm_vma_walk(struct vm_area_struct *vma,
swp_entry_t entry;
pte_t pte = *ptep;
- pfns[i] = 0;
-
if (pte_none(pte)) {
+ if (fault) {
+ pte_unmap(ptep);
+ goto fault;
+ }
pfns[i] = HMM_PFN_EMPTY;
continue;
}
entry = pte_to_swp_entry(pte);
if (!pte_present(pte) && !non_swap_entry(entry)) {
+ if (fault) {
+ pte_unmap(ptep);
+ goto fault;
+ }
+ pfns[i] = 0;
continue;
}
if (pte_present(pte)) {
pfns[i] = hmm_pfn_from_pfn(pte_pfn(pte))|flag;
pfns[i] |= pte_write(pte) ? HMM_PFN_WRITE : 0;
- continue;
- }
-
- /*
- * This is a special swap entry, ignore migration, use
- * device and report anything else as error.
- */
- if (is_device_entry(entry)) {
+ } else if (is_device_entry(entry)) {
+ /* Do not fault device entry */
pfns[i] = hmm_pfn_from_pfn(swp_offset(entry));
if (is_write_device_entry(entry))
pfns[i] |= HMM_PFN_WRITE;
pfns[i] |= HMM_PFN_DEVICE;
pfns[i] |= HMM_PFN_UNADDRESSABLE;
pfns[i] |= flag;
- } else if (!is_migration_entry(entry)) {
+ } else if (is_migration_entry(entry) && fault) {
+ migration_entry_wait(vma->vm_mm, pmdp, addr);
+ /* Start again for current address */
+ next = addr;
+ ptep++;
+ break;
+ } else {
+ /* Report error for everything else */
pfns[i] = HMM_PFN_ERROR;
}
+ if ((fault & pfns[i]) != fault) {
+ pte_unmap(ptep);
+ goto fault;
+ }
}
pte_unmap(ptep - 1);
+ continue;
+
+fault:
+ ret = hmm_vma_do_fault(vma, fault, addr, &pfns[i], block);
+ if (ret)
+ return ret;
+ /* Start again for current address */
+ next = addr;
}
+
+ return 0;
}
/*
@@ -463,7 +570,7 @@ int hmm_vma_get_pfns(struct vm_area_struct *vma,
list_add_rcu(&range->list, &hmm->ranges);
spin_unlock(&hmm->lock);
- hmm_vma_walk(vma, start, end, pfns);
+ hmm_vma_walk(vma, 0, start, end, pfns, false);
return 0;
}
EXPORT_SYMBOL(hmm_vma_get_pfns);
@@ -474,14 +581,22 @@ EXPORT_SYMBOL(hmm_vma_get_pfns);
* @range: range being track
* Returns: false if range data have been invalidated, true otherwise
*
- * Range struct is use to track update to CPU page table after call to
- * hmm_vma_get_pfns(). Once device driver is done using or want to lock update
- * to data it gots from this function it calls hmm_vma_range_done() which stop
- * the tracking.
+ * Range struct is use to track update to CPU page table after call to either
+ * hmm_vma_get_pfns() or hmm_vma_fault(). Once device driver is done using or
+ * want to lock update to data it gots from those functions it must call the
+ * hmm_vma_range_done() function which stop tracking CPU page table update.
+ *
+ * Note that device driver must still implement general CPU page table update
+ * tracking either by using hmm_mirror (see hmm_mirror_register()) or by using
+ * mmu_notifier API directly.
+ *
+ * CPU page table update tracking done through hmm_range is only temporary and
+ * to be use while trying to duplicate CPU page table content for a range of
+ * virtual address.
*
* There is 2 way to use this :
* again:
- * hmm_vma_get_pfns(vma, range, start, end, pfns);
+ * hmm_vma_get_pfns(vma, range, start, end, pfns); or hmm_vma_fault(...);
* trans = device_build_page_table_update_transaction(pfns);
* device_page_table_lock();
* if (!hmm_vma_range_done(vma, range)) {
@@ -492,7 +607,7 @@ EXPORT_SYMBOL(hmm_vma_get_pfns);
* device_page_table_unlock();
*
* Or:
- * hmm_vma_get_pfns(vma, range, start, end, pfns);
+ * hmm_vma_get_pfns(vma, range, start, end, pfns); or hmm_vma_fault(...);
* device_page_table_lock();
* hmm_vma_range_done(vma, range);
* device_update_page_table(pfns);
@@ -521,4 +636,102 @@ bool hmm_vma_range_done(struct vm_area_struct *vma, struct hmm_range *range)
return range->valid;
}
EXPORT_SYMBOL(hmm_vma_range_done);
+
+/*
+ * hmm_vma_fault() - try to fault some address in a virtual address range
+ * @vma: virtual memory area containing the virtual address range
+ * @range: use to track pfns array content validity
+ * @start: fault range virtual start address (inclusive)
+ * @end: fault range virtual end address (exclusive)
+ * @pfns: array of hmm_pfn_t, only entry with fault flag set will be faulted
+ * @write: is it a write fault
+ * @block: allow blocking on fault (if true it sleeps and do not drop mmap_sem)
+ * Returns: 0 success, error otherwise (-EAGAIN means mmap_sem have been drop)
+ *
+ * This is similar to a regular CPU page fault except that it will not trigger
+ * any memory migration if the memory being faulted is not accessible by CPUs.
+ *
+ * On error, for one virtual address in the range, the function will set the
+ * hmm_pfn_t error flag for the corresponding pfn entry.
+ *
+ * Expected use pattern:
+ * retry:
+ * down_read(&mm->mmap_sem);
+ * // Find vma and address device wants to fault, initialize hmm_pfn_t
+ * // array accordingly
+ * ret = hmm_vma_fault(vma, start, end, pfns, allow_retry);
+ * switch (ret) {
+ * case -EAGAIN:
+ * hmm_vma_range_done(vma, range);
+ * // You might want to rate limit or yield to play nicely, you may
+ * // also commit any valid pfn in the array assuming that you are
+ * // getting true from hmm_vma_range_monitor_end()
+ * goto retry;
+ * case 0:
+ * break;
+ * default:
+ * // Handle error !
+ * up_read(&mm->mmap_sem)
+ * return;
+ * }
+ * // Take device driver lock that serialize device page table update
+ * driver_lock_device_page_table_update();
+ * hmm_vma_range_done(vma, range);
+ * // Commit pfns we got from hmm_vma_fault()
+ * driver_unlock_device_page_table_update();
+ * up_read(&mm->mmap_sem)
+ *
+ * YOU MUST CALL hmm_vma_range_done() AFTER THIS FUNCTION RETURN SUCCESS (0)
+ * BEFORE FREEING THE range struct OR YOU WILL HAVE SERIOUS MEMORY CORRUPTION !
+ *
+ * YOU HAVE BEEN WARN !
+ */
+int hmm_vma_fault(struct vm_area_struct *vma,
+ struct hmm_range *range,
+ unsigned long start,
+ unsigned long end,
+ hmm_pfn_t *pfns,
+ bool write,
+ bool block)
+{
+ hmm_pfn_t fault = HMM_PFN_READ | (write ? HMM_PFN_WRITE : 0);
+ struct hmm *hmm;
+ int ret;
+
+ /* Sanity check, this really should not happen ! */
+ if (start < vma->vm_start || start >= vma->vm_end)
+ return -EINVAL;
+ if (end < vma->vm_start || end > vma->vm_end)
+ return -EINVAL;
+
+ hmm = hmm_register(vma->vm_mm);
+ if (!hmm) {
+ hmm_pfns_clear(pfns, start, end);
+ return -ENOMEM;
+ }
+ /* Caller must have register a mirror (with hmm_mirror_register()) ! */
+ if (!hmm->mmu_notifier.ops)
+ return -EINVAL;
+
+ /* Initialize range to track CPU page table update */
+ range->start = start;
+ range->pfns = pfns;
+ range->end = end;
+ spin_lock(&hmm->lock);
+ range->valid = true;
+ list_add_rcu(&range->list, &hmm->ranges);
+ spin_unlock(&hmm->lock);
+
+ /* FIXME support hugetlb fs */
+ if (is_vm_hugetlb_page(vma) || (vma->vm_flags & VM_SPECIAL)) {
+ hmm_pfns_special(pfns, start, end);
+ return 0;
+ }
+
+ ret = hmm_vma_walk(vma, fault, start, end, pfns, block);
+ if (ret)
+ hmm_vma_range_done(vma, range);
+ return ret;
+}
+EXPORT_SYMBOL(hmm_vma_fault);
#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
--
2.4.3
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