2019-08-19 06:41:31

by Christophe Leroy

Subject: [PATCH] powerpc/603: fix handling of the DIRTY flag

If a page is already mapped RW without the DIRTY flag, the DIRTY
flag is never set and a TLB store miss exception is taken forever.

This is easily reproduced with the following app:

void main(void)
{
volatile char *ptr = mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);

*ptr = *ptr;
}

When DIRTY flag is not set, bail out of TLB miss handler and take
a minor page fault which will set the DIRTY flag.

Fixes: f8b58c64eaef ("powerpc/603: let's handle PAGE_DIRTY directly")
Cc: [email protected]
Reported-by: Doug Crawford <[email protected]>
Signed-off-by: Christophe Leroy <[email protected]>
---
arch/powerpc/kernel/head_32.S | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/head_32.S b/arch/powerpc/kernel/head_32.S
index f255e22184b4..534dd2718795 100644
--- a/arch/powerpc/kernel/head_32.S
+++ b/arch/powerpc/kernel/head_32.S
@@ -557,9 +557,9 @@ DataStoreTLBMiss:
cmplw 0,r1,r3
mfspr r2, SPRN_SPRG_PGDIR
#ifdef CONFIG_SWAP
- li r1, _PAGE_RW | _PAGE_PRESENT | _PAGE_ACCESSED
+ li r1, _PAGE_RW | _PAGE_DIRTY | _PAGE_PRESENT | _PAGE_ACCESSED
#else
- li r1, _PAGE_RW | _PAGE_PRESENT
+ li r1, _PAGE_RW | _PAGE_DIRTY | _PAGE_PRESENT
#endif
bge- 112f
lis r2, (swapper_pg_dir - PAGE_OFFSET)@ha /* if kernel address, use */
--
2.13.3

2019-08-22 18:41:26

by Michael Ellerman

Subject: Re: [PATCH] powerpc/603: fix handling of the DIRTY flag

On Mon, 2019-08-19 at 06:40:25 UTC, Christophe Leroy wrote:
> If a page is already mapped RW without the DIRTY flag, the DIRTY
> flag is never set and a TLB store miss exception is taken forever.
>
> This is easily reproduced with the following app:
>
> void main(void)
> {
> volatile char *ptr = mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
>
> *ptr = *ptr;
> }
>
> When DIRTY flag is not set, bail out of TLB miss handler and take
> a minor page fault which will set the DIRTY flag.
>
> Fixes: f8b58c64eaef ("powerpc/603: let's handle PAGE_DIRTY directly")
> Cc: [email protected]
> Reported-by: Doug Crawford <[email protected]>
> Signed-off-by: Christophe Leroy <[email protected]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/415480dce2ef03bb8335deebd2f402f475443ce0

cheers