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[PATCH v6 3/5] xen/arm64: mm: Introduce helpers to prepare/enable/disable the identity mapping

From: Julien Grall <julien@xxxxxxx>

Date: Thu, 2 Mar 2023 14:59:14 +0000

Cc: Luca.Fancellu@xxxxxxx, michal.orzel@xxxxxxx, Julien Grall <jgrall@xxxxxxxxxx>

Delivery-date: Thu, 02 Mar 2023 14:59:26 +0000

List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

From: Julien Grall <jgrall@xxxxxxxxxx> In follow-up patches we will need to have part of Xen identity mapped in order to safely switch the TTBR. On some platform, the identity mapping may have to start at 0. If we always keep the identity region mapped, NULL pointer dereference would lead to access to valid mapping. It would be possible to relocate Xen to avoid clashing with address 0. However the identity mapping is only meant to be used in very limited places. Therefore it would be better to keep the identity region invalid for most of the time. Two new external helpers are introduced: - arch_setup_page_tables() will setup the page-tables so it is easy to create the mapping afterwards. - update_identity_mapping() will create/remove the identity mapping Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx> ---- Changes in v6: - Correctly check the placement of the identity mapping (take 2). - Fix typoes Changes in v5: - The reserved area for the identity mapping is 2TB (so 4 slots) rather than 512GB. Changes in v4: - Fix typo in a comment - Clarify which page-tables are updated Changes in v2: - Remove the arm32 part - Use a different logic for the boot page tables and runtime one because Xen may be running in a different place. --- xen/arch/arm/arm64/Makefile | 1 + xen/arch/arm/arm64/mm.c | 130 ++++++++++++++++++++++++++++ xen/arch/arm/include/asm/arm32/mm.h | 4 + xen/arch/arm/include/asm/arm64/mm.h | 13 +++ xen/arch/arm/include/asm/config.h | 2 + xen/arch/arm/include/asm/setup.h | 11 +++ xen/arch/arm/mm.c | 6 +- 7 files changed, 165 insertions(+), 2 deletions(-) create mode 100644 xen/arch/arm/arm64/mm.c diff --git a/xen/arch/arm/arm64/Makefile b/xen/arch/arm/arm64/Makefile index 6d507da0d44d..28481393e98f 100644 --- a/xen/arch/arm/arm64/Makefile +++ b/xen/arch/arm/arm64/Makefile @@ -10,6 +10,7 @@ obj-y += entry.o obj-y += head.o obj-y += insn.o obj-$(CONFIG_LIVEPATCH) += livepatch.o +obj-y += mm.o obj-y += smc.o obj-y += smpboot.o obj-y += traps.o diff --git a/xen/arch/arm/arm64/mm.c b/xen/arch/arm/arm64/mm.c new file mode 100644 index 000000000000..56b9e9b8d3ef --- /dev/null +++ b/xen/arch/arm/arm64/mm.c @@ -0,0 +1,130 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include <xen/init.h> +#include <xen/mm.h> + +#include <asm/setup.h> + +/* Override macros from asm/page.h to make them work with mfn_t */ +#undef virt_to_mfn +#define virt_to_mfn(va) _mfn(__virt_to_mfn(va)) + +static DEFINE_PAGE_TABLE(xen_first_id); +static DEFINE_PAGE_TABLE(xen_second_id); +static DEFINE_PAGE_TABLE(xen_third_id); + +/* + * The identity mapping may start at physical address 0. So we don't want + * to keep it mapped longer than necessary. + * + * When this is called, we are still using the boot_pgtable. + * + * We need to prepare the identity mapping for both the boot page tables + * and runtime page tables. + * + * The logic to create the entry is slightly different because Xen may + * be running at a different location at runtime. + */ +static void __init prepare_boot_identity_mapping(void) +{ + paddr_t id_addr = virt_to_maddr(_start); + lpae_t pte; + DECLARE_OFFSETS(id_offsets, id_addr); + + /* + * We will be re-using the boot ID tables. They may not have been + * zeroed but they should be unlinked. So it is fine to use + * clear_page(). + */ + clear_page(boot_first_id); + clear_page(boot_second_id); + clear_page(boot_third_id); + + if ( id_offsets[0] >= IDENTITY_MAPPING_AREA_NR_L0 ) + panic("Cannot handle ID mapping above 2TB\n"); + + /* Link first ID table */ + pte = mfn_to_xen_entry(virt_to_mfn(boot_first_id), MT_NORMAL); + pte.pt.table = 1; + pte.pt.xn = 0; + + write_pte(&boot_pgtable[id_offsets[0]], pte); + + /* Link second ID table */ + pte = mfn_to_xen_entry(virt_to_mfn(boot_second_id), MT_NORMAL); + pte.pt.table = 1; + pte.pt.xn = 0; + + write_pte(&boot_first_id[id_offsets[1]], pte); + + /* Link third ID table */ + pte = mfn_to_xen_entry(virt_to_mfn(boot_third_id), MT_NORMAL); + pte.pt.table = 1; + pte.pt.xn = 0; + + write_pte(&boot_second_id[id_offsets[2]], pte); + + /* The mapping in the third table will be created at a later stage */ +} + +static void __init prepare_runtime_identity_mapping(void) +{ + paddr_t id_addr = virt_to_maddr(_start); + lpae_t pte; + DECLARE_OFFSETS(id_offsets, id_addr); + + if ( id_offsets[0] >= IDENTITY_MAPPING_AREA_NR_L0 ) + panic("Cannot handle ID mapping above 2TB\n"); + + /* Link first ID table */ + pte = pte_of_xenaddr((vaddr_t)xen_first_id); + pte.pt.table = 1; + pte.pt.xn = 0; + + write_pte(&xen_pgtable[id_offsets[0]], pte); + + /* Link second ID table */ + pte = pte_of_xenaddr((vaddr_t)xen_second_id); + pte.pt.table = 1; + pte.pt.xn = 0; + + write_pte(&xen_first_id[id_offsets[1]], pte); + + /* Link third ID table */ + pte = pte_of_xenaddr((vaddr_t)xen_third_id); + pte.pt.table = 1; + pte.pt.xn = 0; + + write_pte(&xen_second_id[id_offsets[2]], pte); + + /* The mapping in the third table will be created at a later stage */ +} + +void __init arch_setup_page_tables(void) +{ + prepare_boot_identity_mapping(); + prepare_runtime_identity_mapping(); +} + +void update_identity_mapping(bool enable) +{ + paddr_t id_addr = virt_to_maddr(_start); + int rc; + + if ( enable ) + rc = map_pages_to_xen(id_addr, maddr_to_mfn(id_addr), 1, + PAGE_HYPERVISOR_RX); + else + rc = destroy_xen_mappings(id_addr, id_addr + PAGE_SIZE); + + BUG_ON(rc); +} + +/* + * Local variables: + * mode: C + * c-file-style: "BSD" + * c-basic-offset: 4 + * indent-tabs-mode: nil + * End: + */ diff --git a/xen/arch/arm/include/asm/arm32/mm.h b/xen/arch/arm/include/asm/arm32/mm.h index 8bfc906e7178..856f2dbec4ad 100644 --- a/xen/arch/arm/include/asm/arm32/mm.h +++ b/xen/arch/arm/include/asm/arm32/mm.h @@ -18,6 +18,10 @@ static inline bool arch_mfns_in_directmap(unsigned long mfn, unsigned long nr) bool init_domheap_mappings(unsigned int cpu); +static inline void arch_setup_page_tables(void) +{ +} + #endif /* __ARM_ARM32_MM_H__ */ /* diff --git a/xen/arch/arm/include/asm/arm64/mm.h b/xen/arch/arm/include/asm/arm64/mm.h index aa2adac63189..e0bd23a6ed0c 100644 --- a/xen/arch/arm/include/asm/arm64/mm.h +++ b/xen/arch/arm/include/asm/arm64/mm.h @@ -1,6 +1,8 @@ #ifndef __ARM_ARM64_MM_H__ #define __ARM_ARM64_MM_H__ +extern DEFINE_PAGE_TABLE(xen_pgtable); + /* * On ARM64, all the RAM is currently direct mapped in Xen. * Hence return always true. @@ -10,6 +12,17 @@ static inline bool arch_mfns_in_directmap(unsigned long mfn, unsigned long nr) return true; } +void arch_setup_page_tables(void); + +/* + * Enable/disable the identity mapping in the live page-tables (i.e. + * the one pointed by TTBR_EL2). + * + * Note that nested call (e.g. enable=true, enable=true) is not + * supported. + */ +void update_identity_mapping(bool enable); + #endif /* __ARM_ARM64_MM_H__ */ /* diff --git a/xen/arch/arm/include/asm/config.h b/xen/arch/arm/include/asm/config.h index e388462c23d1..f02733e40a87 100644 --- a/xen/arch/arm/include/asm/config.h +++ b/xen/arch/arm/include/asm/config.h @@ -179,6 +179,8 @@ #else /* ARM_64 */ +#define IDENTITY_MAPPING_AREA_NR_L0 4 + #define VMAP_VIRT_START GB(1) #define VMAP_VIRT_SIZE GB(1) diff --git a/xen/arch/arm/include/asm/setup.h b/xen/arch/arm/include/asm/setup.h index a926f30a2be4..66b27f2b57c1 100644 --- a/xen/arch/arm/include/asm/setup.h +++ b/xen/arch/arm/include/asm/setup.h @@ -166,6 +166,17 @@ u32 device_tree_get_u32(const void *fdt, int node, int map_range_to_domain(const struct dt_device_node *dev, u64 addr, u64 len, void *data); +extern DEFINE_BOOT_PAGE_TABLE(boot_pgtable); + +#ifdef CONFIG_ARM_64 +extern DEFINE_BOOT_PAGE_TABLE(boot_first_id); +#endif +extern DEFINE_BOOT_PAGE_TABLE(boot_second_id); +extern DEFINE_BOOT_PAGE_TABLE(boot_third_id); + +/* Find where Xen will be residing at runtime and return a PT entry */ +lpae_t pte_of_xenaddr(vaddr_t); + extern const char __ro_after_init_start[], __ro_after_init_end[]; struct init_info diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c index 9263fedc3b7d..265bc082567e 100644 --- a/xen/arch/arm/mm.c +++ b/xen/arch/arm/mm.c @@ -93,7 +93,7 @@ DEFINE_BOOT_PAGE_TABLE(boot_third); #ifdef CONFIG_ARM_64 #define HYP_PT_ROOT_LEVEL 0 -static DEFINE_PAGE_TABLE(xen_pgtable); +DEFINE_PAGE_TABLE(xen_pgtable); static DEFINE_PAGE_TABLE(xen_first); #define THIS_CPU_PGTABLE xen_pgtable #else @@ -388,7 +388,7 @@ void flush_page_to_ram(unsigned long mfn, bool sync_icache) invalidate_icache(); } -static inline lpae_t pte_of_xenaddr(vaddr_t va) +lpae_t pte_of_xenaddr(vaddr_t va) { paddr_t ma = va + phys_offset; @@ -495,6 +495,8 @@ void __init setup_pagetables(unsigned long boot_phys_offset) phys_offset = boot_phys_offset; + arch_setup_page_tables(); + #ifdef CONFIG_ARM_64 pte = pte_of_xenaddr((uintptr_t)xen_first); pte.pt.table = 1; -- 2.39.1

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