Re: [PATCH v7 14/21] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages

[Christoph Hellwig]

On Wed, Jun 15, 2022 at 10:12:26AM -0600, Logan Gunthorpe wrote:
> GUP Callers that expect PCI P2PDMA pages can now set FOLL_PCI_P2PDMA to
> allow obtaining P2PDMA pages. If GUP is called without the flag and a
> P2PDMA page is found, it will return an error.
> 
> FOLL_PCI_P2PDMA cannot be set if FOLL_LONGTERM is set.

Looks good:

Reviewed-by: Christoph Hellwig 
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[PATCH v7 14/21] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages

[Logan Gunthorpe]

GUP Callers that expect PCI P2PDMA pages can now set FOLL_PCI_P2PDMA to
allow obtaining P2PDMA pages. If GUP is called without the flag and a
P2PDMA page is found, it will return an error.

FOLL_PCI_P2PDMA cannot be set if FOLL_LONGTERM is set.

Signed-off-by: Logan Gunthorpe 
---
 include/linux/mm.h |  1 +
 mm/gup.c   | 22 +-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index bc8f326be0ce..0bcb54ea503c 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2941,6 +2941,7 @@ struct page *follow_page(struct vm_area_struct *vma, 
unsigned long address,
 #define FOLL_SPLIT_PMD 0x2 /* split huge pmd before returning */
 #define FOLL_PIN   0x4 /* pages must be released via unpin_user_page */
 #define FOLL_FAST_ONLY 0x8 /* gup_fast: prevent fall-back to slow gup */
+#define FOLL_PCI_P2PDMA0x10 /* allow returning PCI P2PDMA pages */
 
 /*
  * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each
diff --git a/mm/gup.c b/mm/gup.c
index 551264407624..f15f01d06a09 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -564,6 +564,12 @@ static struct page *follow_page_pte(struct vm_area_struct 
*vma,
goto out;
}
 
+   if (unlikely(!(flags & FOLL_PCI_P2PDMA) &&
+is_pci_p2pdma_page(page))) {
+   page = ERR_PTR(-EREMOTEIO);
+   goto out;
+   }
+
VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
   !PageAnonExclusive(page), page);
 
@@ -994,6 +1000,9 @@ static int check_vma_flags(struct vm_area_struct *vma, 
unsigned long gup_flags)
if ((gup_flags & FOLL_LONGTERM) && vma_is_fsdax(vma))
return -EOPNOTSUPP;
 
+   if ((gup_flags & FOLL_LONGTERM) && (gup_flags & FOLL_PCI_P2PDMA))
+   return -EOPNOTSUPP;
+
if (vma_is_secretmem(vma))
return -EFAULT;
 
@@ -2289,6 +2298,10 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, 
unsigned long end,
VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
page = pte_page(pte);
 
+   if (unlikely(!(flags & FOLL_PCI_P2PDMA) &&
+is_pci_p2pdma_page(page)))
+   goto pte_unmap;
+
folio = try_grab_folio(page, 1, flags);
if (!folio)
goto pte_unmap;
@@ -2368,6 +2381,12 @@ static int __gup_device_huge(unsigned long pfn, unsigned 
long addr,
undo_dev_pagemap(nr, nr_start, flags, pages);
break;
}
+
+   if (!(flags & FOLL_PCI_P2PDMA) && is_pci_p2pdma_page(page)) {
+   undo_dev_pagemap(nr, nr_start, flags, pages);
+   break;
+   }
+
SetPageReferenced(page);
pages[*nr] = page;
if (unlikely(!try_grab_page(page, flags))) {
@@ -2856,7 +2875,8 @@ static int internal_get_user_pages_fast(unsigned long 
start,
 
if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM |
   FOLL_FORCE | FOLL_PIN | FOLL_GET |
-  FOLL_FAST_ONLY | FOLL_NOFAULT)))
+  FOLL_FAST_ONLY | FOLL_NOFAULT |
+  FOLL_PCI_P2PDMA)))
return -EINVAL;
 
if (gup_flags & FOLL_PIN)
-- 
2.30.2

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