From: Fangyu Yu <[email protected]> Crash kexec uses riscv_kexec_norelocate as a trampoline to jump into the crashkernel. Pre-build dedicated 4 KB page tables in machine_kexec_prepare() that map the trampoline page as executable, so the panic path only has to switch satp and jump.
Two mappings are installed into a shared pgd: - VA(__kexec_tramp_text_start) -> PA(__kexec_tramp_text_start) - PA(__kexec_tramp_text_start) -> PA(__kexec_tramp_text_start) The lower-level tables (p4d/pud/pmd/pte) are shared between both mappings; map_tramp_page() walks the existing tree and only populates entries that are still zero, so the two installs coexist even when their indices happen to collide at any level. Signed-off-by: Fangyu Yu <[email protected]> --- arch/riscv/kernel/machine_kexec.c | 87 +++++++++++++++++++++++++++++++ 1 file changed, 87 insertions(+) diff --git a/arch/riscv/kernel/machine_kexec.c b/arch/riscv/kernel/machine_kexec.c index e6e179cffc44..1947b7bdf5c4 100644 --- a/arch/riscv/kernel/machine_kexec.c +++ b/arch/riscv/kernel/machine_kexec.c @@ -18,6 +18,85 @@ #include <linux/interrupt.h> #include <linux/irq.h> +/* + * Trampoline page tables. Both the VA(trampoline)->PA and the + * PA(trampoline)->PA identity mapping are installed in this single + * pgd; the lower-level tables are shared so the two mappings can + * coexist even if they happen to collide at any level (the walker + * only populates entries that are still zero). + * + * Pre-allocate for the largest paging mode (Sv57). Levels that the + * runtime mode does not use simply waste a page or two of BSS, in + * exchange for a builder that is infallible and safe to run from + * the panic path. + */ +static pgd_t kexec_tramp_pgd[PTRS_PER_PGD] __aligned(PAGE_SIZE); +#ifdef CONFIG_64BIT +static p4d_t kexec_tramp_p4d[PTRS_PER_P4D] __aligned(PAGE_SIZE); +static pud_t kexec_tramp_pud[PTRS_PER_PUD] __aligned(PAGE_SIZE); +static pmd_t kexec_tramp_pmd[PTRS_PER_PMD] __aligned(PAGE_SIZE); +#endif +static pte_t kexec_tramp_pte[PTRS_PER_PTE] __aligned(PAGE_SIZE); + +static void map_tramp_page(unsigned long va, unsigned long pa) +{ + pgd_t *pgd = kexec_tramp_pgd + pgd_index(va); + +#ifdef CONFIG_64BIT + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + + if (pgtable_l5_enabled) { + if (pgd_val(*pgd) == 0) + set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa_symbol(kexec_tramp_p4d)), + PAGE_TABLE)); + p4d = kexec_tramp_p4d + p4d_index(va); + } else { + p4d = (p4d_t *)pgd; + } + + if (pgtable_l4_enabled) { + if (p4d_val(*p4d) == 0) + set_p4d(p4d, pfn_p4d(PFN_DOWN(__pa_symbol(kexec_tramp_pud)), + PAGE_TABLE)); + pud = kexec_tramp_pud + pud_index(va); + } else { + pud = (pud_t *)p4d; + } + + if (pud_val(*pud) == 0) + set_pud(pud, pfn_pud(PFN_DOWN(__pa_symbol(kexec_tramp_pmd)), + PAGE_TABLE)); + pmd = kexec_tramp_pmd + pmd_index(va); + + if (pmd_val(*pmd) == 0) + set_pmd(pmd, pfn_pmd(PFN_DOWN(__pa_symbol(kexec_tramp_pte)), + PAGE_TABLE)); +#else + /* Sv32: PGD points directly to the PTE table. */ + if (pgd_val(*pgd) == 0) + set_pgd(pgd, pfn_pgd(PFN_DOWN(__pa_symbol(kexec_tramp_pte)), + PAGE_TABLE)); +#endif + + set_pte(kexec_tramp_pte + pte_index(va), + pfn_pte(PFN_DOWN(pa), PAGE_KERNEL_EXEC)); +} + +static void riscv_kexec_build_tramp(unsigned long va, unsigned long pa) +{ + /* VA -> PA: map the trampoline page via its kernel VA. */ + map_tramp_page(va, pa); + + /* + * PA -> PA: identity-map the same page so the second-pass code + * can keep executing after the kernel VA mapping is dropped. + */ + map_tramp_page(pa, pa); +} + + /* * machine_kexec_prepare - Initialize kexec * @@ -73,6 +152,14 @@ machine_kexec_prepare(struct kimage *image) /* Mark the control page executable */ set_memory_x((unsigned long) control_code_buffer, 1); + } else { + /* + * Crash kexec uses riscv_kexec_norelocate as a trampoline. + * Pre-build the trampoline page tables here so the panic + * path only has to switch satp and jump. + */ + riscv_kexec_build_tramp((unsigned long)__kexec_tramp_text_start, + __pa_symbol(__kexec_tramp_text_start)); } return 0; -- 2.50.1
