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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [PATCH v3 15/18] xen/arm64: mm: Introduce helpers to prepare/enable/disable the identity mapping
On Mon, 12 Dec 2022, Julien Grall wrote:
> 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 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 | 121 ++++++++++++++++++++++++++++
> xen/arch/arm/include/asm/arm32/mm.h | 4 +
> xen/arch/arm/include/asm/arm64/mm.h | 12 +++
> xen/arch/arm/include/asm/setup.h | 11 +++
> xen/arch/arm/mm.c | 6 +-
> 6 files changed, 153 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..9eaf545ea9dd
> --- /dev/null
> +++ b/xen/arch/arm/arm64/mm.c
> @@ -0,0 +1,121 @@
> +/* 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);
> +
> + if ( id_offsets[0] != 0 )
> + panic("Cannot handled ID mapping above 512GB\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] != 0 )
> + panic("Cannot handled ID mapping above 512GB\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..807d3b2321fd 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 +12,16 @@ 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
> + *
> + * Note that nested a 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/setup.h
> b/xen/arch/arm/include/asm/setup.h
> index fdbf68aadcaa..e7a80fecec14 100644
> --- a/xen/arch/arm/include/asm/setup.h
> +++ b/xen/arch/arm/include/asm/setup.h
> @@ -168,6 +168,17 @@ int map_range_to_domain(const struct dt_device_node *dev,
>
> extern const char __ro_after_init_start[], __ro_after_init_end[];
>
> +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);
This is more a matter of taste but I would either:
- define extern all BOOT_PAGE_TABLEs here both ARM64 and ARM32 with
#ifdefs
- or define all the ARM64 only BOOT_PAGE_TABLE in arm64/mm.h and all the
ARM32 only BOOT_PAGE_TABLE in arm32/mm.h
Right now we have a mix, as we have boot_first_id with a #ifdef here
and we have xen_pgtable in arm64/mm.h
Also we are missing boot_second and boot_third. We might as well be
consistent and declare them all?
> +/* Find where Xen will be residing at runtime and return an PT entry */
> +lpae_t pte_of_xenaddr(vaddr_t);
> +
> #endif
> /*
> * Local variables:
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 0cf7ad4f0e8c..39e0d9e03c9c 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;
> --
> 2.38.1
>
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