[RFC RESEND 01/16] mm/hmm: let users to tag specific PFNs

Leon Romanovsky
2024-03-05T11:18:58Z

From: Leon Romanovsky <leonro@nvidia.com>

Introduce new sticky flag, which isn't overwritten by HMM range fault.
Such flag allows users to tag specific PFNs with extra data in addition
to already filled by HMM.

Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
include/linux/hmm.h | 3 +++
mm/hmm.c | 34 +++++++++++++++++++++-------------
2 files changed, 24 insertions(+), 13 deletions(-)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index 126a36571667..b90902baa593 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -23,6 +23,7 @@ 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_STICKY - Flag preserved on input-to-output transformation
*
* On input:
* 0 - Return the current state of the page, do not fault it.
@@ -36,6 +37,8 @@ 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 lag, carried from Input to Output */
+ HMM_PFN_STICKY = 1UL << (BITS_PER_LONG - 7),
HMM_PFN_ORDER_SHIFT = (BITS_PER_LONG - 8),

/* Input flags */
diff --git a/mm/hmm.c b/mm/hmm.c
index 277ddcab4947..9645a72beec0 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -44,8 +44,10 @@ static int hmm_pfns_fill(unsigned long addr, unsigned long end,
{
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_STICKY;
+ range->hmm_pfns[i] |= cpu_flags;
+ }
return 0;
}

@@ -202,8 +204,10 @@ 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_STICKY;
+ hmm_pfns[i] |= pfn | cpu_flags;
+ }
return 0;
}
#else /* CONFIG_TRANSPARENT_HUGEPAGE */
@@ -236,7 +240,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0);
if (required_fault)
goto fault;
- *hmm_pfn = 0;
+ *hmm_pfn = *hmm_pfn & HMM_PFN_STICKY;
return 0;
}

@@ -253,14 +257,14 @@ 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;
+ *hmm_pfn = (*hmm_pfn & HMM_PFN_STICKY) | swp_offset_pfn(entry) | cpu_flags;
return 0;
}

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

@@ -304,11 +308,11 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr,
pte_unmap(ptep);
return -EFAULT;
}
- *hmm_pfn = HMM_PFN_ERROR;
+ *hmm_pfn = (*hmm_pfn & HMM_PFN_STICKY) | HMM_PFN_ERROR;
return 0;
}

- *hmm_pfn = pte_pfn(pte) | cpu_flags;
+ *hmm_pfn = (*hmm_pfn & HMM_PFN_STICKY) | pte_pfn(pte) | cpu_flags;
return 0;

fault:
@@ -453,8 +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_STICKY;
+ hmm_pfns[i] |= pfn | cpu_flags;
+ }
goto out_unlock;
}

@@ -512,8 +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_STICKY;
+ range->hmm_pfns[i] |= pfn | cpu_flags;
+ }

spin_unlock(ptl);
return 0;
--
2.44.0