On 2016/7/12 23:46, Eric W. Biederman wrote: > zhongjiang <[email protected]> writes: > >> From: zhong jiang <[email protected]> >> >> when image is loaded into kernel, we need set up page table for it. and >> all valid pfn also set up new mapping. it will tend to establish a pmd >> page table in the form of a large page if pud_present is true. >> relocate_kernel >> points to code segment can locate in the pmd huge entry in >> init_transtion_pgtable. >> therefore, we need to take the situation into account. > I can see how in theory this might be necessary but when is a kernel virtual > address on x86_64 that is above 0x8000000000000000 in conflict with an > identity mapped physicall address that are all below 0x8000000000000000? > > If anything the code could be simplified to always assume those mappings > are unoccupied. > > Did you run into an actual failure somewhere? > > Eric > I do not understand what you trying to say, Maybe I miss your point. The key is how to ensure that relocate_kernel points to the pmd entry is not huge page. Thanks zhongjiang >> Signed-off-by: zhong jiang <[email protected]> >> --- >> arch/x86/kernel/machine_kexec_64.c | 20 ++++++++++++++++++-- >> 1 file changed, 18 insertions(+), 2 deletions(-) >> >> diff --git a/arch/x86/kernel/machine_kexec_64.c >> b/arch/x86/kernel/machine_kexec_64.c >> index 5a294e4..c33e344 100644 >> --- a/arch/x86/kernel/machine_kexec_64.c >> +++ b/arch/x86/kernel/machine_kexec_64.c >> @@ -14,6 +14,7 @@ >> #include <linux/gfp.h> >> #include <linux/reboot.h> >> #include <linux/numa.h> >> +#include <linux/hugetlb.h> >> #include <linux/ftrace.h> >> #include <linux/io.h> >> #include <linux/suspend.h> >> @@ -34,6 +35,17 @@ static struct kexec_file_ops *kexec_file_loaders[] = { >> }; >> #endif >> >> +static void split_pmd(pmd_t *pmd, pte_t *pte) >> +{ >> + unsigned long pfn = pmd_pfn(*pmd); >> + int i = 0; >> + >> + do { >> + set_pte(pte, pfn_pte(pfn, PAGE_KERNEL_EXEC)); >> + pfn++; >> + } while (pte++, i++, i < PTRS_PER_PTE); >> +} >> + >> static void free_transition_pgtable(struct kimage *image) >> { >> free_page((unsigned long)image->arch.pud); >> @@ -68,15 +80,19 @@ static int init_transition_pgtable(struct kimage *image, >> pgd_t *pgd) >> set_pud(pud, __pud(__pa(pmd) | _KERNPG_TABLE)); >> } >> pmd = pmd_offset(pud, vaddr); >> - if (!pmd_present(*pmd)) { >> + if (!pmd_present(*pmd) || pmd_huge(*pmd)) { >> pte = (pte_t *)get_zeroed_page(GFP_KERNEL); >> if (!pte) >> goto err; >> image->arch.pte = pte; >> - set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE)); >> + if (pmd_huge(*pmd)) >> + split_pmd(pmd, pte); >> + else >> + set_pmd(pmd, __pmd(__pa(pte) | _KERNPG_TABLE)); >> } >> pte = pte_offset_kernel(pmd, vaddr); >> set_pte(pte, pfn_pte(paddr >> PAGE_SHIFT, PAGE_KERNEL_EXEC)); >> + >> return 0; >> err: >> free_transition_pgtable(image); > . >
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