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

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

[Christophe Leroy]

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: stable@vger.kernel.org
Reported-by: Doug Crawford <doug.crawford@intelight-its.com>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
---
 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

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

[Michael Ellerman]

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: stable@vger.kernel.org
> Reported-by: Doug Crawford <doug.crawford@intelight-its.com>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>

Applied to powerpc next, thanks.

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

cheers