Subject: [PATCH v2] ARM: mm: Get rid ofL_PTE_USER ref from PAGE_S2_DEVICE

From: [email-masked] (Marc Zyngier)
Date: Sat, 25 May 2013 12:02:33 +0200

On Fri, 24 May 2013 18:12:39 -0700, Christoffer Dall
<[email-masked]> wrote:
> THe L_PTE_USER actually has nothing to do with stage 2 mappings and the
> L_PTE_S2_RDWR value sets the readable bit, which was what L_PTE_USER
> was used for before proper handling of stage 2 memory defines.
> 
> Changelog:
>  [v2]: Change default mappings to be r/w instead of r/o, as per Marc
>        Zyngier's suggestion.
> 
> Cc: Marc Zyngier <[email-masked]>
> Signed-off-by: Christoffer Dall <[email-masked]>
> ---
>  arch/arm/include/asm/pgtable.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/pgtable.h
> b/arch/arm/include/asm/pgtable.h
> index 9bcd262..8afc60c 100644
> --- a/arch/arm/include/asm/pgtable.h
> +++ b/arch/arm/include/asm/pgtable.h
> @@ -97,7 +97,7 @@ extern pgprot_t		pgprot_s2_device;
>  #define PAGE_HYP		_MOD_PROT(pgprot_kernel, L_PTE_HYP)
>  #define PAGE_HYP_DEVICE		_MOD_PROT(pgprot_hyp_device, L_PTE_HYP)
>  #define PAGE_S2			_MOD_PROT(pgprot_s2, L_PTE_S2_RDONLY)
> -#define PAGE_S2_DEVICE		_MOD_PROT(pgprot_s2_device, L_PTE_USER |
> L_PTE_S2_RDONLY)
> +#define PAGE_S2_DEVICE		_MOD_PROT(pgprot_s2_device, L_PTE_S2_RDWR)
>  
>  #define __PAGE_NONE		__pgprot(_L_PTE_DEFAULT | L_PTE_RDONLY | L_PTE_XN
|
>  L_PTE_NONE)
>  #define __PAGE_SHARED		__pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_XN)

Actually, there's a much better solution.

Just get rid of PAGE_S2_DEVICE altogether, as it is completely useless. We
never have to enforce a memory type in S2 that is stronger than the guest's
view. If the guest insists on doing something silly (mapping a device as
normal memory, for example), we really don't have to fix things for them.

See the patch I posted a while ago as part of my pending fixes series:
https://lists.cs.columbia.edu/pipermail/kvmarm/2013-May/005827.html

        M.
-- 
Who you jivin' with that Cosmik Debris?