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Message-Id: <1719478388-31917-1-git-send-email-yangge1116@126.com>
Date: Thu, 27 Jun 2024 16:53:08 +0800
From: yangge1116@....com
To: akpm@...ux-foundation.org
Cc: linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
stable@...r.kernel.org,
21cnbao@...il.com,
peterx@...hat.com,
baolin.wang@...ux.alibaba.com,
liuzixing@...on.cn,
yangge <yangge1116@....com>
Subject: [PATCH] mm/gup: Use try_grab_page() instead of try_grab_folio() in gup slow path
From: yangge <yangge1116@....com>
If a large number of CMA memory are configured in system (for
example, the CMA memory accounts for 50% of the system memory),
starting a SEV virtual machine will fail. During starting the SEV
virtual machine, it will call pin_user_pages_fast(..., FOLL_LONGTERM,
...) to pin memory. Normally if a page is present and in CMA area,
pin_user_pages_fast() will first call __get_user_pages_locked() to
pin the page in CMA area, and then call
check_and_migrate_movable_pages() to migrate the page from CMA area
to non-CMA area. But the current code calling __get_user_pages_locked()
will fail, because it call try_grab_folio() to pin page in gup slow
path.
The commit 57edfcfd3419 ("mm/gup: accelerate thp gup even for "pages
!= NULL"") uses try_grab_folio() in gup slow path, which seems to be
problematic because try_grap_folio() will check if the page can be
longterm pinned. This check may fail and cause __get_user_pages_lock()
to fail. However, these checks are not required in gup slow path,
seems we can use try_grab_page() instead of try_grab_folio(). In
addition, in the current code, try_grab_page() can only add 1 to the
page's refcount. We extend this function so that the page's refcount
can be increased according to the parameters passed in.
The following log reveals it:
[ 464.325306] WARNING: CPU: 13 PID: 6734 at mm/gup.c:1313 __get_user_pages+0x423/0x520
[ 464.325464] CPU: 13 PID: 6734 Comm: qemu-kvm Kdump: loaded Not tainted 6.6.33+ #6
[ 464.325477] RIP: 0010:__get_user_pages+0x423/0x520
[ 464.325515] Call Trace:
[ 464.325520] <TASK>
[ 464.325523] ? __get_user_pages+0x423/0x520
[ 464.325528] ? __warn+0x81/0x130
[ 464.325536] ? __get_user_pages+0x423/0x520
[ 464.325541] ? report_bug+0x171/0x1a0
[ 464.325549] ? handle_bug+0x3c/0x70
[ 464.325554] ? exc_invalid_op+0x17/0x70
[ 464.325558] ? asm_exc_invalid_op+0x1a/0x20
[ 464.325567] ? __get_user_pages+0x423/0x520
[ 464.325575] __gup_longterm_locked+0x212/0x7a0
[ 464.325583] internal_get_user_pages_fast+0xfb/0x190
[ 464.325590] pin_user_pages_fast+0x47/0x60
[ 464.325598] sev_pin_memory+0xca/0x170 [kvm_amd]
[ 464.325616] sev_mem_enc_register_region+0x81/0x130 [kvm_amd]
Fixes: 57edfcfd3419 ("mm/gup: accelerate thp gup even for "pages != NULL"")
Cc: <stable@...r.kernel.org>
Signed-off-by: yangge <yangge1116@....com>
---
mm/gup.c | 26 ++++++++++++--------------
mm/huge_memory.c | 2 +-
mm/internal.h | 2 +-
3 files changed, 14 insertions(+), 16 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 6ff9f95..bb58909 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -222,7 +222,7 @@ static void gup_put_folio(struct folio *folio, int refs, unsigned int flags)
* -ENOMEM FOLL_GET or FOLL_PIN was set, but the page could not
* be grabbed.
*/
-int __must_check try_grab_page(struct page *page, unsigned int flags)
+int __must_check try_grab_page(struct page *page, int refs, unsigned int flags)
{
struct folio *folio = page_folio(page);
@@ -233,7 +233,7 @@ int __must_check try_grab_page(struct page *page, unsigned int flags)
return -EREMOTEIO;
if (flags & FOLL_GET)
- folio_ref_inc(folio);
+ folio_ref_add(folio, refs);
else if (flags & FOLL_PIN) {
/*
* Don't take a pin on the zero page - it's not going anywhere
@@ -248,13 +248,13 @@ int __must_check try_grab_page(struct page *page, unsigned int flags)
* so that the page really is pinned.
*/
if (folio_test_large(folio)) {
- folio_ref_add(folio, 1);
- atomic_add(1, &folio->_pincount);
+ folio_ref_add(folio, refs);
+ atomic_add(refs, &folio->_pincount);
} else {
- folio_ref_add(folio, GUP_PIN_COUNTING_BIAS);
+ folio_ref_add(folio, refs * GUP_PIN_COUNTING_BIAS);
}
- node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, 1);
+ node_stat_mod_folio(folio, NR_FOLL_PIN_ACQUIRED, refs);
}
return 0;
@@ -729,7 +729,7 @@ static struct page *follow_huge_pud(struct vm_area_struct *vma,
gup_must_unshare(vma, flags, page))
return ERR_PTR(-EMLINK);
- ret = try_grab_page(page, flags);
+ ret = try_grab_page(page, 1, flags);
if (ret)
page = ERR_PTR(ret);
else
@@ -806,7 +806,7 @@ static struct page *follow_huge_pmd(struct vm_area_struct *vma,
VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) &&
!PageAnonExclusive(page), page);
- ret = try_grab_page(page, flags);
+ ret = try_grab_page(page, 1, flags);
if (ret)
return ERR_PTR(ret);
@@ -969,7 +969,7 @@ static struct page *follow_page_pte(struct vm_area_struct *vma,
!PageAnonExclusive(page), page);
/* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */
- ret = try_grab_page(page, flags);
+ ret = try_grab_page(page, 1, flags);
if (unlikely(ret)) {
page = ERR_PTR(ret);
goto out;
@@ -1233,7 +1233,7 @@ static int get_gate_page(struct mm_struct *mm, unsigned long address,
goto unmap;
*page = pte_page(entry);
}
- ret = try_grab_page(*page, gup_flags);
+ ret = try_grab_page(*page, 1, gup_flags);
if (unlikely(ret))
goto unmap;
out:
@@ -1636,22 +1636,20 @@ static long __get_user_pages(struct mm_struct *mm,
* pages.
*/
if (page_increm > 1) {
- struct folio *folio;
/*
* Since we already hold refcount on the
* large folio, this should never fail.
*/
- folio = try_grab_folio(page, page_increm - 1,
+ ret = try_grab_page(page, page_increm - 1,
foll_flags);
- if (WARN_ON_ONCE(!folio)) {
+ if (WARN_ON_ONCE(ret)) {
/*
* Release the 1st page ref if the
* folio is problematic, fail hard.
*/
gup_put_folio(page_folio(page), 1,
foll_flags);
- ret = -EFAULT;
goto out;
}
}
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 425374a..18604e4 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1332,7 +1332,7 @@ struct page *follow_devmap_pmd(struct vm_area_struct *vma, unsigned long addr,
if (!*pgmap)
return ERR_PTR(-EFAULT);
page = pfn_to_page(pfn);
- ret = try_grab_page(page, flags);
+ ret = try_grab_page(page, 1, flags);
if (ret)
page = ERR_PTR(ret);
diff --git a/mm/internal.h b/mm/internal.h
index 2ea9a88..5305bbf 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1227,7 +1227,7 @@ int migrate_device_coherent_page(struct page *page);
* mm/gup.c
*/
struct folio *try_grab_folio(struct page *page, int refs, unsigned int flags);
-int __must_check try_grab_page(struct page *page, unsigned int flags);
+int __must_check try_grab_page(struct page *page, int refs, unsigned int flags);
/*
* mm/huge_memory.c
--
2.7.4
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