Re: [Qemu-devel] [PATCH v4] target-mips: fix updating XContext on mmu exception

[James Hogan <james.hogan@imgtec.com>]

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On Thu, Oct 29, 2015 at 05:17:52PM +0000, Yongbok Kim wrote:
> Correct updating XContext.Region field on mmu exceptions.
> If Config3.CTXTC = 0 then the R field of XContext has to be updated
> with the value of bits 63..62 of the virtual address upon a TLB
> exception.

It wouldn't hurt to mention how the existing behaviour is wrong, since
it requires a little staring (and counting of zeros) to see it, i.e.
that the old mask incorrectly selected bits 47:46 of the address, and
shifted them down into the middle of BadVPN2.

> Also fixed the below line which overs 80 characters.
> 
> Signed-off-by: Yongbok Kim <yongbok.kim@imgtec.com>

Reviewed-by: James Hogan <james.hogan@imgtec.com>

Cheers
James

> ---
>  target-mips/helper.c |    7 ++++---
>  1 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/target-mips/helper.c b/target-mips/helper.c
> index 2d86323..b3fe816 100644
> --- a/target-mips/helper.c
> +++ b/target-mips/helper.c
> @@ -293,9 +293,10 @@ static void raise_mmu_exception(CPUMIPSState *env, target_ulong address,
>          (env->CP0_EntryHi & 0xFF) | (address & (TARGET_PAGE_MASK << 1));
>  #if defined(TARGET_MIPS64)
>      env->CP0_EntryHi &= env->SEGMask;
> -    env->CP0_XContext = (env->CP0_XContext & ((~0ULL) << (env->SEGBITS - 7))) |
> -                        ((address & 0xC00000000000ULL) >> (55 - env->SEGBITS)) |
> -                        ((address & ((1ULL << env->SEGBITS) - 1) & 0xFFFFFFFFFFFFE000ULL) >> 9);
> +    env->CP0_XContext =
> +        /* PTEBase */   (env->CP0_XContext & ((~0ULL) << (env->SEGBITS - 7))) |
> +        /* R */         (extract64(address, 62, 2) << (env->SEGBITS - 9)) |
> +        /* BadVPN2 */   (extract64(address, 13, env->SEGBITS - 13) << 4);
>  #endif
>      cs->exception_index = exception;
>      env->error_code = error_code;
> -- 
> 1.7.1
> 
> 

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