[PATCH v2] ARM: mm: Get rid of L_PTE_USER ref from PAGE_S2_DEVICE

[PATCH v2] ARM: mm: Get rid of L_PTE_USER ref from PAGE_S2_DEVICE

[Christoffer Dall]

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 <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
---
 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)
-- 
1.7.9.5

[PATCH v2] ARM: mm: Get rid of L_PTE_USER ref from PAGE_S2_DEVICE

[Marc Zyngier]

On Fri, 24 May 2013 18:12:39 -0700, Christoffer Dall
<cdall@cs.columbia.edu> 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 <marc.zyngier@arm.com>
> Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
> ---
>  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?

[PATCH v2] ARM: mm: Get rid of L_PTE_USER ref from PAGE_S2_DEVICE

[Christoffer Dall]

On Sat, May 25, 2013 at 3:02 AM, Marc Zyngier <maz@misterjones.org> wrote:
> On Fri, 24 May 2013 18:12:39 -0700, Christoffer Dall
> <cdall@cs.columbia.edu> 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 <marc.zyngier@arm.com>
>> Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
>> ---
>>  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
>
yeah duh, I'll reply to that one.