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Re: [Qemu-devel] [PATCH] target-s390x: fix LOAD MULTIPLE instruction on

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH] target-s390x: fix LOAD MULTIPLE instruction on page boundary
Date: Thu, 21 May 2015 14:42:07 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 05/21/2015 02:32 PM, Aurelien Jarno wrote:
> When consecutive memory locations are on page boundary a page fault
> might occur when using the LOAD MULTIPLE instruction. In that case real
> hardware doesn't load any register.
> This is an important detail in case the base register is in the list
> of registers to be loaded. If a page fault occurs this register might be
> overwritten and when the instruction is later restarted the wrong
> base register value is useD.
> Fix this by first loading all values from memory and then writing them
> back to the registers.
> This fixes random segmentation faults seen in the guest.
> Cc: Alexander Graf <address@hidden>
> Cc: Richard Henderson <address@hidden>
> Signed-off-by: Aurelien Jarno <address@hidden>
> ---
>  target-s390x/translate.c | 56 
> +++++++++++++++++++++++++++++++++++++++++++-----
>  1 file changed, 51 insertions(+), 5 deletions(-)

Hmm.  Seems to be un/under-specified in the PoO.  That said,

Reviewed-by: Richard Henderson <address@hidden>

It would be nice to know if there ought to be similar up-front access checking
for STM, to avoid errant partial stores.


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