[PATCH v7 10/17] mm/hmm: let users to tag specific PFN with DMA mapped bit

Leon Romanovsky
2025-02-05T14:41:29Z

From: Leon Romanovsky <leonro@nvidia.com>

Introduce new sticky flag (HMM_PFN_DMA_MAPPED), which isn't overwritten
by HMM range fault. Such flag allows users to tag specific PFNs with
information if this specific PFN was already DMA mapped.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
include/linux/hmm.h | 17 +++++++++++++++
mm/hmm.c | 51 ++++++++++++++++++++++++++++-----------------
2 files changed, 49 insertions(+), 19 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 126a36571667..a1ddbedc19c0 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -23,6 +23,8 @@ struct mmu_interval_notifier;
* HMM_PFN_WRITE - if the page memory can be written to (requires HMM_PFN_VALID)
* HMM_PFN_ERROR - accessing the pfn is impossible and the device should
* fail. ie poisoned memory, special pages, no vma, etc
+ * HMM_PFN_DMA_MAPPED - Flag preserved on input-to-output transformation
+ * to mark that page is already DMA mapped
*
* On input:
* 0 - Return the current state of the page, do not fault it.
@@ -36,6 +38,13 @@ enum hmm_pfn_flags {
HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
+
+ /*
+ * Sticky flags, carried from input to output,
+ * don't forget to update HMM_PFN_INOUT_FLAGS
+ */
+ HMM_PFN_DMA_MAPPED = 1UL << (BITS_PER_LONG - 7),
+
HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 8),

/* Input flags */
@@ -57,6 +66,14 @@ static inline struct page *hmm_pfn_to_page(unsigned long hmm_pfn)
return pfn_to_page(hmm_pfn & ~HMM_PFN_FLAGS);
}

+/*
+ * hmm_pfn_to_phys() - return physical address pointed to by a device entry
+ */
+static inline phys_addr_t hmm_pfn_to_phys(unsigned long hmm_pfn)
+{
+ return __pfn_to_phys(hmm_pfn & ~HMM_PFN_FLAGS);
+}
+
/*
* hmm_pfn_to_map_order() - return the CPU mapping size order
*
diff --git a/mm/hmm.c b/mm/hmm.c
index 7e0229ae4a5a..da5743f6d854 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -39,13 +39,20 @@ enum {
HMM_NEED_ALL_BITS = HMM_NEED_FAULT | HMM_NEED_WRITE_FAULT,
};

+enum {
+ /* These flags are carried from input-to-output */
+ HMM_PFN_INOUT_FLAGS = HMM_PFN_DMA_MAPPED,
+};
+
static int hmm_pfns_fill(unsigned long addr, unsigned long end,
struct hmm_range *range, unsigned long cpu_flags)
{
unsigned long i = (addr - range->start) >> PAGE_SHIFT;

- for (; addr < end; addr += PAGE_SIZE, i++)
- range->hmm_pfns[i] = cpu_flags;
+ for (; addr < end; addr += PAGE_SIZE, i++) {
+ range->hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
+ range->hmm_pfns[i] |= cpu_flags;
+ }
return 0;
}

@@ -202,8 +209,10 @@ static int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr,
return hmm_vma_fault(addr, end, required_fault, walk);

pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
- for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++)
- hmm_pfns[i] = pfn | cpu_flags;
+ for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) {
+ hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
+ hmm_pfns[i] |= pfn | cpu_flags;
+ }
return 0;
}
#else /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -230,14 +239,14 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
unsigned long cpu_flags;
pte_t pte = ptep_get(ptep);
uint64_t pfn_req_flags = *hmm_pfn;
+ uint64_t new_pfn_flags = 0;

if (pte_none_mostly(pte)) {
required_fault =
hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
if (required_fault)
goto fault;
- *hmm_pfn = 0;
- return 0;
+ goto out;
}

if (!pte_present(pte)) {
@@ -253,16 +262,14 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
cpu_flags = HMM_PFN_VALID;
if (is_writable_device_private_entry(entry))
cpu_flags |= HMM_PFN_WRITE;
- *hmm_pfn = swp_offset_pfn(entry) | cpu_flags;
- return 0;
+ new_pfn_flags = swp_offset_pfn(entry) | cpu_flags;
+ goto out;
}

required_fault =
hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
- if (!required_fault) {
- *hmm_pfn = 0;
- return 0;
- }
+ if (!required_fault)
+ goto out;

if (!non_swap_entry(entry))
goto fault;
@@ -304,11 +311,13 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
pte_unmap(ptep);
return -EFAULT;
}
- *hmm_pfn = HMM_PFN_ERROR;
- return 0;
+ new_pfn_flags = HMM_PFN_ERROR;
+ goto out;
}

- *hmm_pfn = pte_pfn(pte) | cpu_flags;
+ new_pfn_flags = pte_pfn(pte) | cpu_flags;
+out:
+ *hmm_pfn = (*hmm_pfn & HMM_PFN_INOUT_FLAGS) | new_pfn_flags;
return 0;

fault:
@@ -448,8 +457,10 @@ static int hmm_vma_walk_pud(pud_t *pudp, unsigned long start, unsigned long end,
}

pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
- for (i = 0; i < npages; ++i, ++pfn)
- hmm_pfns[i] = pfn | cpu_flags;
+ for (i = 0; i < npages; ++i, ++pfn) {
+ hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
+ hmm_pfns[i] |= pfn | cpu_flags;
+ }
goto out_unlock;
}

@@ -507,8 +518,10 @@ static int hmm_vma_walk_hugetlb_entry(pte_t *pte, unsigned long hmask,
}

pfn = pte_pfn(entry) + ((start & ~hmask) >> PAGE_SHIFT);
- for (; addr < end; addr += PAGE_SIZE, i++, pfn++)
- range->hmm_pfns[i] = pfn | cpu_flags;
+ for (; addr < end; addr += PAGE_SIZE, i++, pfn++) {
+ range->hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS;
+ range->hmm_pfns[i] |= pfn | cpu_flags;
+ }

spin_unlock(ptl);
return 0;
--
2.48.1