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

Catalin Marinas
2013-01-24T17:14:07Z

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.

--
Catalin