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SubjectRe: [RFC PATCH] kexec, x86/boot: map systab region in identity mapping before accessing it
On 04/19/19 at 04:34pm, Kairui Song wrote:
> /* Locates and clears a region for a new top level page table. */
> void initialize_identity_maps(void)
> {
> - /* If running as an SEV guest, the encryption mask is required. */
> - set_sev_encryption_mask();
> -
> - /* Exclude the encryption mask from __PHYSICAL_MASK */
> - physical_mask &= ~sme_me_mask;
> -
> - /* Init mapping_info with run-time function/buffer pointers. */
> - mapping_info.alloc_pgt_page = alloc_pgt_page;
> - mapping_info.context = &pgt_data;
> - mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
> - mapping_info.kernpg_flag = _KERNPG_TABLE;
> -
> - /*
> - * It should be impossible for this not to already be true,
> - * but since calling this a second time would rewind the other
> - * counters, let's just make sure this is reset too.
> - */
> - pgt_data.pgt_buf_offset = 0;
> -
> - /*
> - * If we came here via startup_32(), cr3 will be _pgtable already
> - * and we must append to the existing area instead of entirely
> - * overwriting it.
> - *
> - * With 5-level paging, we use '_pgtable' to allocate the p4d page table,
> - * the top-level page table is allocated separately.
> - *
> - * p4d_offset(top_level_pgt, 0) would cover both the 4- and 5-level
> - * cases. On 4-level paging it's equal to 'top_level_pgt'.
> - */
> - top_level_pgt = read_cr3_pa();
> - if (p4d_offset((pgd_t *)top_level_pgt, 0) == (p4d_t *)_pgtable) {
> - debug_putstr("booted via startup_32()\n");
> - pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
> - pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
> - memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
> - } else {
> - debug_putstr("booted via startup_64()\n");
> - pgt_data.pgt_buf = _pgtable;
> - pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
> - memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
> + top_level_pgt = early_boot_top_pgt;
> + if ((p4d_t *)top_level_pgt != (p4d_t *)_pgtable)
> top_level_pgt = (unsigned long)alloc_pgt_page(&pgt_data);

Kairui, will you make a patchset to include these changes separately
later on? I don't get the purposes of code changes. E.g here, I
don't know why you introduce a new variable early_boot_top_pgt, and
allocate the page table, even though they have been done in the old
initialize_identity_maps().

Thanks
Baoquan

> - }
> }
>
> /*
> @@ -141,8 +41,7 @@ void add_identity_map(unsigned long start, unsigned long size)
> return;
>
> /* Build the mapping. */
> - kernel_ident_mapping_init(&mapping_info, (pgd_t *)top_level_pgt,
> - start, end);
> + add_identity_map_pgd(start, end, top_level_pgt);
> }
>
> /*
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index c0d6c560df69..6b3548080d15 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -345,6 +345,8 @@ asmlinkage __visible void *extract_kernel(void *rmode, memptr heap,
> const unsigned long kernel_total_size = VO__end - VO__text;
> unsigned long virt_addr = LOAD_PHYSICAL_ADDR;
>
> + initialize_pgtable_alloc();
> +
> /* Retain x86 boot parameters pointer passed from startup_32/64. */
> boot_params = rmode;
>
> diff --git a/arch/x86/boot/compressed/pgtable.h b/arch/x86/boot/compressed/pgtable.h
> index 6ff7e81b5628..443df2b65fbf 100644
> --- a/arch/x86/boot/compressed/pgtable.h
> +++ b/arch/x86/boot/compressed/pgtable.h
> @@ -16,5 +16,16 @@ extern unsigned long *trampoline_32bit;
>
> extern void trampoline_32bit_src(void *return_ptr);
>
> +extern struct alloc_pgt_data pgt_data;
> +
> +extern unsigned long early_boot_top_pgt;
> +
> +void *alloc_pgt_page(void *context);
> +
> +int add_identity_map_pgd(unsigned long pstart,
> + unsigned long pend, unsigned long pgd);
> +
> +void initialize_pgtable_alloc(void);
> +
> #endif /* __ASSEMBLER__ */
> #endif /* BOOT_COMPRESSED_PAGETABLE_H */
> diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> index f8debf7aeb4c..cd36cf9e6a5c 100644
> --- a/arch/x86/boot/compressed/pgtable_64.c
> +++ b/arch/x86/boot/compressed/pgtable_64.c
> @@ -1,9 +1,30 @@
> +/*
> + * Since we're dealing with identity mappings, physical and virtual
> + * addresses are the same, so override these defines which are ultimately
> + * used by the headers in misc.h.
> + */
> +#define __pa(x) ((unsigned long)(x))
> +#define __va(x) ((void *)((unsigned long)(x)))
> +
> +/* No PAGE_TABLE_ISOLATION support needed either: */
> +#undef CONFIG_PAGE_TABLE_ISOLATION
> +
> +#include "misc.h"
> +#include "pgtable.h"
> +#include "../string.h"
> +
> #include <linux/efi.h>
> #include <asm/e820/types.h>
> #include <asm/processor.h>
> #include <asm/efi.h>
> -#include "pgtable.h"
> -#include "../string.h"
> +
> +/* For handling early ident mapping */
> +#include <asm/init.h>
> +#include <asm/pgtable.h>
> +/* Use the static base for this part of the boot process */
> +#undef __PAGE_OFFSET
> +#define __PAGE_OFFSET __PAGE_OFFSET_BASE
> +#include "../../mm/ident_map.c"
>
> /*
> * __force_order is used by special_insns.h asm code to force instruction
> @@ -14,6 +35,28 @@
> */
> unsigned long __force_order;
>
> +/* Used to track our page table allocation area. */
> +struct alloc_pgt_data {
> + unsigned char *pgt_buf;
> + unsigned long pgt_buf_size;
> + unsigned long pgt_buf_offset;
> +};
> +
> +/* Used to track our allocated page tables. */
> +struct alloc_pgt_data pgt_data;
> +
> +/* Track the first loaded boot page table. */
> +unsigned long early_boot_top_pgt;
> +
> +phys_addr_t physical_mask = (1ULL << __PHYSICAL_MASK_SHIFT) - 1;
> +
> +/*
> + * Mapping information structure passed to kernel_ident_mapping_init().
> + * Due to relocation, pointers must be assigned at run time not build time.
> + */
> +static struct x86_mapping_info mapping_info;
> +
> +/* For handling trampoline. */
> #define BIOS_START_MIN 0x20000U /* 128K, less than this is insane */
> #define BIOS_START_MAX 0x9f000U /* 640K, absolute maximum */
>
> @@ -202,3 +245,87 @@ void cleanup_trampoline(void *pgtable)
> /* Restore trampoline memory */
> memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
> }
> +
> +/*
> + * Allocates space for a page table entry, using struct alloc_pgt_data
> + * above. Besides the local callers, this is used as the allocation
> + * callback in mapping_info below.
> + */
> +void *alloc_pgt_page(void *context)
> +{
> + struct alloc_pgt_data *pages = (struct alloc_pgt_data *)context;
> + unsigned char *entry;
> +
> + /* Validate there is space available for a new page. */
> + if (pages->pgt_buf_offset >= pages->pgt_buf_size) {
> + debug_putstr("out of pgt_buf in " __FILE__ "!?\n");
> + debug_putaddr(pages->pgt_buf_offset);
> + debug_putaddr(pages->pgt_buf_size);
> + return NULL;
> + }
> +
> + entry = pages->pgt_buf + pages->pgt_buf_offset;
> + pages->pgt_buf_offset += PAGE_SIZE;
> +
> + return entry;
> +}
> +
> +/* Locates and clears a region for update or create page table. */
> +void initialize_pgtable_alloc(void)
> +{
> + /* If running as an SEV guest, the encryption mask is required. */
> + set_sev_encryption_mask();
> +
> + /* Exclude the encryption mask from __PHYSICAL_MASK */
> + physical_mask &= ~sme_me_mask;
> +
> + /* Init mapping_info with run-time function/buffer pointers. */
> + mapping_info.alloc_pgt_page = alloc_pgt_page;
> + mapping_info.context = &pgt_data;
> + mapping_info.page_flag = __PAGE_KERNEL_LARGE_EXEC | sme_me_mask;
> + mapping_info.kernpg_flag = _KERNPG_TABLE;
> +
> + /*
> + * It should be impossible for this not to already be true,
> + * but since calling this a second time would rewind the other
> + * counters, let's just make sure this is reset too.
> + */
> + pgt_data.pgt_buf_offset = 0;
> +
> + /*
> + * If we came here via startup_32(), cr3 will be _pgtable already
> + * and we must append to the existing area instead of entirely
> + * overwriting it.
> + *
> + * With 5-level paging, we use '_pgtable' to allocate the p4d page
> + * table, the top-level page table is allocated separately.
> + *
> + * p4d_offset(early_boot_top_pgt, 0) would cover both the 4- and 5-level
> + * cases. On 4-level paging it's equal to 'early_boot_top_pgt'.
> + */
> +
> + early_boot_top_pgt = read_cr3_pa();
> + early_boot_top_pgt = (unsigned long)p4d_offset(
> + (pgd_t *)early_boot_top_pgt, 0);
> + if ((p4d_t *)early_boot_top_pgt == (p4d_t *)_pgtable) {
> + debug_putstr("booted via startup_32()\n");
> + pgt_data.pgt_buf = _pgtable + BOOT_INIT_PGT_SIZE;
> + pgt_data.pgt_buf_size = BOOT_PGT_SIZE - BOOT_INIT_PGT_SIZE;
> + memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
> + } else {
> + debug_putstr("booted via startup_64()\n");
> + pgt_data.pgt_buf = _pgtable;
> + pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
> + memset(pgt_data.pgt_buf, 0, pgt_data.pgt_buf_size);
> + }
> +}
> +
> +/*
> + * Helper for mapping extra memory region in very early stage
> + * before extract and execute the actual kernel
> + */
> +int add_identity_map_pgd(unsigned long pstart, unsigned long pend,
> + unsigned long pgd)
> +{
> + kernel_ident_mapping_init(&mapping_info, (pgd_t *)pgd, pstart, pend);
> +}
> diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
> index 680c320363db..fb37eb98b65d 100644
> --- a/arch/x86/include/asm/boot.h
> +++ b/arch/x86/include/asm/boot.h
> @@ -33,6 +33,8 @@
> #ifdef CONFIG_X86_64
> # define BOOT_STACK_SIZE 0x4000
>
> +/* Reserve one page for possible extra mapping requirement */
> +# define BOOT_EXTRA_PGT_SIZE (1*4096)
> # define BOOT_INIT_PGT_SIZE (6*4096)
> # ifdef CONFIG_RANDOMIZE_BASE
> /*
> @@ -43,12 +45,12 @@
> * Total is 19 pages.
> */
> # ifdef CONFIG_X86_VERBOSE_BOOTUP
> -# define BOOT_PGT_SIZE (19*4096)
> +# define BOOT_PGT_SIZE ((19 * 4096) + BOOT_EXTRA_PGT_SIZE)
> # else /* !CONFIG_X86_VERBOSE_BOOTUP */
> -# define BOOT_PGT_SIZE (17*4096)
> +# define BOOT_PGT_SIZE ((17 * 4096) + BOOT_EXTRA_PGT_SIZE)
> # endif
> # else /* !CONFIG_RANDOMIZE_BASE */
> -# define BOOT_PGT_SIZE BOOT_INIT_PGT_SIZE
> +# define BOOT_PGT_SIZE (BOOT_INIT_PGT_SIZE + BOOT_EXTRA_PGT_SIZE)
> # endif
>
> #else /* !CONFIG_X86_64 */
> --
> 2.20.1
>

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