Re: [PATCH v6 01/15] ARM: Add page table and page defines needed by KVM

Christoffer Dall
2013-01-24T17:25:43Z

On Thu, Jan 24, 2013 at 12:13 PM, Catalin Marinas
<catalin.marinas@arm.com> wrote:
> On Thu, Jan 24, 2013 at 05:04:32PM +0000, Christoffer Dall wrote:
>> On Thu, Jan 24, 2013 at 12:02 PM, Catalin Marinas
>> <catalin.marinas@arm.com> wrote:
>> > On Thu, Jan 24, 2013 at 04:05:33PM +0000, Christoffer Dall wrote:
>> >> On Thu, Jan 24, 2013 at 6:39 AM, Catalin Marinas
>> >> <catalin.marinas@arm.com> wrote:
>> >> > On Wed, Jan 16, 2013 at 05:57:26PM +0000, Christoffer Dall wrote:
>> >> >> @@ -82,6 +85,10 @@ extern pgprot_t pgprot_kernel;
>> >> >> #define PAGE_READONLY_EXEC _MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_RDONLY)
>> >> >> #define PAGE_KERNEL _MOD_PROT(pgprot_kernel, L_PTE_XN)
>> >> >> #define PAGE_KERNEL_EXEC pgprot_kernel
>> >> >> +#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)
>> >> >
>> >> > Are these S2 read-only by default?
>> >>
>> >> not sure I understand what you're asking here?
>> >
>> > Why do you pass L_PTE_S2_RDONLY? Do you need to restrict guest writes
>> > via the stage 2 attributes?
>> >
>> yes, for example when KSM merges two pages, then it must be mapped
>> read-only to the guest so that we catch writes and perform COW.
>
> OK, so you want the default to be read-only unless write access is
> required and you perform an 'or' with L_PTE_S2_RDWR. Sounds fine.
>
exactly, the specific pointer to the code is in line ~562 in arch/arm/kvm/mmu.c.

-Christoffer