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Subject[PATCH v4 15/23] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages
Callers that expect PCI P2PDMA pages can now set FOLL_PCI_P2PDMA to
allow obtaining P2PDMA pages. If a caller does not set this flag
and tries to map P2PDMA pages it will fail.

This is implemented by checking failing if PCI p2pdma pages are
found when FOLL_PCI_P2PDMA is set. This is only done if pte_devmap()
is set.

FOLL_PCI_P2PDMA cannot be set if FOLL_LONGTERM is set.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
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 a7e4a9e7d807..65cb27cebbab 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2971,6 +2971,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address,
#define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */
#define FOLL_PIN 0x40000 /* pages must be released via unpin_user_page */
#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */
+#define FOLL_PCI_P2PDMA 0x100000 /* 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 2c51e9748a6a..c31461c3d256 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -527,6 +527,12 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
page = pte_page(pte);
else
goto no_page;
+
+ if (unlikely(!(flags & FOLL_PCI_P2PDMA) &&
+ is_pci_p2pdma_page(page))) {
+ page = ERR_PTR(-EREMOTEIO);
+ goto out;
+ }
} else if (unlikely(!page)) {
if (flags & FOLL_DUMP) {
/* Avoid special (like zero) pages in core dumps */
@@ -980,6 +986,9 @@ 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;

@@ -2297,6 +2306,10 @@ 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(pte_devmap(pte) && !(flags & FOLL_PCI_P2PDMA) &&
+ is_pci_p2pdma_page(page)))
+ goto pte_unmap;
+
head = try_grab_compound_head(page, 1, flags);
if (!head)
goto pte_unmap;
@@ -2374,6 +2387,12 @@ 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))) {
@@ -2842,7 +2861,8 @@ 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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