On 12/13/19 12:47 PM, Sean Christopherson wrote:
+unsigned long dev_pagemap_mapping_shift(unsigned long address, + struct mm_struct *mm) +{ + pgd_t *pgd; + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + + pgd = pgd_offset(mm, address); + if (!pgd_present(*pgd)) + return 0; + p4d = p4d_offset(pgd, address); + if (!p4d_present(*p4d)) + return 0; + pud = pud_offset(p4d, address); + if (!pud_present(*pud)) + return 0; + if (pud_devmap(*pud)) + return PUD_SHIFT; + pmd = pmd_offset(pud, address); + if (!pmd_present(*pmd)) + return 0; + if (pmd_devmap(*pmd)) + return PMD_SHIFT; + pte = pte_offset_map(pmd, address); + if (!pte_present(*pte)) + return 0; + if (pte_devmap(*pte)) + return PAGE_SHIFT; + return 0; +} +EXPORT_SYMBOL_GPL(dev_pagemap_mapping_shift);This is basically a rehash of lookup_address_in_pgd(), and doesn't provide exactly what KVM needs. E.g. KVM works with levels instead of shifts, and it would be nice to provide the pte so that KVM can sanity check that the pfn from this walk matches the pfn it plans on mapping.
One minor issue is that the levels for lookup_address_in_pgd() and for KVM differ in name, although not in value. lookup uses PG_LEVEL_4K = 1. KVM uses PT_PAGE_TABLE_LEVEL = 1. The enums differ a little too: x86 has a name for a 512G page, etc. It's all in arch/x86.
Does KVM-x86 need its own names for the levels? If not, I could convert the PT_PAGE_TABLE_* stuff to PG_LEVEL_* stuff.
Instead of exporting dev_pagemap_mapping_shift(), what about replacing it with a patch to introduce lookup_address_mm() and export that? dev_pagemap_mapping_shift() could then wrap the new helper (if you want),
I might hold off on that for now, since that helper is used outside of x86, and I don't know if 'level' makes sense outside of x86.
Thanks, Barret
