Re: [Qemu-devel] [PATCH v2 06/10] target-mips: Set target page size to 16K in KVM mode

[Aurelien Jarno <aurelien@aurel32.net>]

On Mon, Dec 16, 2013 at 02:12:41PM +0000, James Hogan wrote:
> From: Sanjay Lal <sanjayl@kymasys.com>
> 
> With larger set associative caches KVM can open the possibility of cache
> aliasing between the memory that QEMU allocates with mmap and the
> mapping into the guest address space. Therefore increase the target page
> size to 16K when KVM is configured.
> 
> Signed-off-by: Sanjay Lal <sanjayl@kymasys.com>
> Signed-off-by: James Hogan <james.hogan@imgtec.com>
> Cc: Aurelien Jarno <aurelien@aurel32.net>
> ---
> Changes in v2:
>  - Expand commit message
> ---
>  target-mips/mips-defs.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/target-mips/mips-defs.h b/target-mips/mips-defs.h
> index bf094a3..473ddf8 100644
> --- a/target-mips/mips-defs.h
> +++ b/target-mips/mips-defs.h
> @@ -5,7 +5,12 @@
>  //#define USE_HOST_FLOAT_REGS
>  
>  /* Real pages are variable size... */
> +#ifdef CONFIG_KVM
> +/* For KVM/MIPS the minimum page size is 16K due to cache aliasing issues */
> +#define TARGET_PAGE_BITS 14
> +#else
>  #define TARGET_PAGE_BITS 12
> +#endif
>  #define MIPS_TLB_MAX 128
>  
>  #if defined(TARGET_MIPS64)

I am not sure it is something correct. It means that the emulated CPU
won't support 4K pages anymore, even when running in TCG mode without
KVM. If the kernel maps a 4K page, in practice a 16K page is going to be
mapped by the qemu tlb.

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net