From: John Starks <jostarks@microsoft.com>

For dax pud, pud_huge() returns true on x86. So the function works as long
as hugetlb is configured. However, dax doesn't depend on hugetlb.
Commit 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") fixed
devmap-backed huge PMDs, but missed devmap-backed huge PUDs. Fix this as
well.

This fixes the below kernel panic:

general protection fault, probably for non-canonical address 0x69e7c000cc478: 0000 [#1] SMP
	< snip >
Call Trace:
<TASK>
get_user_pages_fast+0x1f/0x40
iov_iter_get_pages+0xc6/0x3b0
? mempool_alloc+0x5d/0x170
bio_iov_iter_get_pages+0x82/0x4e0
? bvec_alloc+0x91/0xc0
? bio_alloc_bioset+0x19a/0x2a0
blkdev_direct_IO+0x282/0x480
? __io_complete_rw_common+0xc0/0xc0
? filemap_range_has_page+0x82/0xc0
generic_file_direct_write+0x9d/0x1a0
? inode_update_time+0x24/0x30
__generic_file_write_iter+0xbd/0x1e0
blkdev_write_iter+0xb4/0x150
? io_import_iovec+0x8d/0x340
io_write+0xf9/0x300
io_issue_sqe+0x3c3/0x1d30
? sysvec_reschedule_ipi+0x6c/0x80
__io_queue_sqe+0x33/0x240
? fget+0x76/0xa0
io_submit_sqes+0xe6a/0x18d0
? __fget_light+0xd1/0x100
__x64_sys_io_uring_enter+0x199/0x880
? __context_tracking_enter+0x1f/0x70
? irqentry_exit_to_user_mode+0x24/0x30
? irqentry_exit+0x1d/0x30
? __context_tracking_exit+0xe/0x70
do_syscall_64+0x3b/0x90
entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7fc97c11a7be
	< snip >
</TASK>
---[ end trace 48b2e0e67debcaeb ]---
RIP: 0010:internal_get_user_pages_fast+0x340/0x990
	< snip >
Kernel panic - not syncing: Fatal exception
Kernel Offset: disabled

Fixes: 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax")
Signed-off-by: John Starks <jostarks@microsoft.com>
Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
---
 mm/gup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index c2c2c6d..e776540 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2765,7 +2765,7 @@ static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned lo
 		next = pud_addr_end(addr, end);
 		if (unlikely(!pud_present(pud)))
 			return 0;
-		if (unlikely(pud_huge(pud))) {
+		if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
 			if (!gup_huge_pud(pud, pudp, addr, next, flags,
 					  pages, nr))
 				return 0;
-- 
1.8.3.1

On Tue,  6 Dec 2022 22:00:53 -0800 Saurabh Sengar <ssengar@linux.microsoft.com> wrote:

> From: John Starks <jostarks@microsoft.com>
> 
> For dax pud, pud_huge() returns true on x86. So the function works as long
> as hugetlb is configured. However, dax doesn't depend on hugetlb.
> Commit 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") fixed
> devmap-backed huge PMDs, but missed devmap-backed huge PUDs. Fix this as
> well.
> 
> This fixes the below kernel panic:
> 
> ...
>
> Fixes: 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax")

Feb 2019.

> Signed-off-by: John Starks <jostarks@microsoft.com>
> Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> ---
>  mm/gup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index c2c2c6d..e776540 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2765,7 +2765,7 @@ static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned lo
>  		next = pud_addr_end(addr, end);
>  		if (unlikely(!pud_present(pud)))
>  			return 0;
> -		if (unlikely(pud_huge(pud))) {
> +		if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
>  			if (!gup_huge_pud(pud, pudp, addr, next, flags,
>  					  pages, nr))
>  				return 0;

I assume this should be backported into -stable kernels?

On Wed, Dec 07, 2022 at 01:31:30PM -0800, Andrew Morton wrote:
> On Tue,  6 Dec 2022 22:00:53 -0800 Saurabh Sengar <ssengar@linux.microsoft.com> wrote:
> 
> > From: John Starks <jostarks@microsoft.com>
> > 
> > For dax pud, pud_huge() returns true on x86. So the function works as long
> > as hugetlb is configured. However, dax doesn't depend on hugetlb.
> > Commit 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax") fixed
> > devmap-backed huge PMDs, but missed devmap-backed huge PUDs. Fix this as
> > well.
> > 
> > This fixes the below kernel panic:
> > 
> > ...
> >
> > Fixes: 414fd080d125 ("mm/gup: fix gup_pmd_range() for dax")
> 
> Feb 2019.
> 
> > Signed-off-by: John Starks <jostarks@microsoft.com>
> > Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
> > ---
> >  mm/gup.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/mm/gup.c b/mm/gup.c
> > index c2c2c6d..e776540 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2765,7 +2765,7 @@ static int gup_pud_range(p4d_t *p4dp, p4d_t p4d, unsigned long addr, unsigned lo
> >  		next = pud_addr_end(addr, end);
> >  		if (unlikely(!pud_present(pud)))
> >  			return 0;
> > -		if (unlikely(pud_huge(pud))) {
> > +		if (unlikely(pud_huge(pud) || pud_devmap(pud))) {
> >  			if (!gup_huge_pud(pud, pudp, addr, next, flags,
> >  					  pages, nr))
> >  				return 0;
> 
> I assume this should be backported into -stable kernels?
That would be helpful, thanks.