[linux-yocto] [PATCH] powerpc/603: Fix handling of the DIRTY flag

[Bruce Ashfield]

In message: [linux-yocto][PATCH] powerpc/603: Fix handling of the DIRTY flag
on 24/09/2019 zhe.he at windriver.com wrote:

> From: Christophe Leroy <christophe.leroy at c-s.fr>
> 
> commit 415480dce2ef03bb8335deebd2f402f475443ce0 upstream
> 
> 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 at vger.kernel.org # v5.1+
> Reported-by: Doug Crawford <doug.crawford at intelight-its.com>
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> Link: https://lore.kernel.org/r/80432f71194d7ee75b2f5043ecf1501cf1cca1f3.1566196646.git.christophe.leroy@c-s.fr
> Signed-off-by: He Zhe <zhe.he at windriver.com>
> ---
> This is for v5.2/standard/fsl-mpc8315e-rdb. It fixes potential system hang
> without any direct warning or error which has not been observed on qemuppc.
> 
> It has not been ported to stable tree.

but at least is has been cc'd to stable. I'll watch for it to show up in my
future 5.2 -stabe updates.

Cheers,

Bruce

> 
>  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 f255e22..534dd27 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 */
> -- 
> 2.7.4
>