ARM: kvm: define PAGE_S2_DEVICE as read-only by default

Now that we support read-only memslots, we need to make sure that
pass-through device mappings are not mapped writable if the guest
has requested them to be read-only. The existing implementation
already honours this by calling kvm_set_s2pte_writable() on the new
pte in case of writable mappings, so all we need to do is define
the default pgprot_t value used for devices to be PTE_S2_RDONLY.
Acked-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NChristoffer Dall <christoffer.dall@linaro.org>

arch/arm/include/asm/pgtable.h

@@ -100,7 +100,7 @@ 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_S2_RDWR)
+#define PAGE_S2_DEVICE		_MOD_PROT(pgprot_s2_device, L_PTE_S2_RDONLY)
 
 #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)