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From: Lai Jiangshan on 15 Jul 2010 22:20

a light weight version of get_user_page_and_protection()

Signed-off-by: Lai Jiangshan <laijs(a)cn.fujitsu.com>
---
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index a34c785..d0e4f2f 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -618,6 +618,8 @@ static inline void clone_pgd_range(pgd_t *dst, pgd_t *src, int count)
memcpy(dst, src, count * sizeof(pgd_t));
}

+extern
+struct page *get_user_page_and_protection(unsigned long addr, int *writable);

#include <asm-generic/pgtable.h>
#endif /* __ASSEMBLY__ */
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 6382140..de44847 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -1832,23 +1832,6 @@ static void kvm_unsync_pages(struct kvm_vcpu *vcpu, gfn_t gfn)
}
}

-/* get a current mapped page fast, and test whether the page is writable. */
-static struct page *get_user_page_and_protection(unsigned long addr,
- int *writable)
-{
- struct page *page[1];
-
- if (__get_user_pages_fast(addr, 1, 1, page) == 1) {
- *writable = 1;
- return page[0];
- }
- if (__get_user_pages_fast(addr, 1, 0, page) == 1) {
- *writable = 0;
- return page[0];
- }
- return NULL;
-}
-
static pfn_t kvm_get_pfn_for_page_fault(struct kvm *kvm, gfn_t gfn,
int write_fault, int *host_writable)
{
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
index a4ce19f..34b05c7 100644
--- a/arch/x86/mm/gup.c
+++ b/arch/x86/mm/gup.c
@@ -275,7 +275,6 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,

return nr;
}
-EXPORT_SYMBOL_GPL(__get_user_pages_fast);

/**
* get_user_pages_fast() - pin user pages in memory
@@ -375,3 +374,83 @@ slow_irqon:
return ret;
}
}
+
+/*
+ * get a current mapped page fast, and test whether the page is writable.
+ * equivalent version(but slower):
+ * {
+ * struct page *page[1];
+ *
+ * if (__get_user_pages_fast(addr, 1, 1, page) == 1) {
+ * *writable = 1;
+ * return page[0];
+ * }
+ * if (__get_user_pages_fast(addr, 1, 0, page) == 1) {
+ * *writable = 0;
+ * return page[0];
+ * }
+ * return NULL;
+ * }
+ */
+struct page *get_user_page_and_protection(unsigned long addr, int *writable)
+{
+ unsigned long flags;
+ struct mm_struct *mm = current->mm;
+ pgd_t *pgdp;
+ pud_t *pudp;
+ pmd_t *pmdp;
+ pte_t pte, *ptep;
+
+ unsigned long mask = _PAGE_PRESENT | _PAGE_USER;
+ unsigned long offset = 0;
+ struct page *head, *page = NULL;
+
+ addr &= PAGE_MASK;
+
+ local_irq_save(flags);
+ pgdp = pgd_offset(mm, addr);
+ if (!pgd_present(*pgdp))
+ goto out;
+
+ pudp = pud_offset(pgdp, addr);
+ if (!pud_present(*pudp))
+ goto out;
+
+ if (unlikely(pud_large(*pudp))) {
+ pte = *(pte_t *)pudp;
+ offset = ((addr & ~PUD_MASK) >> PAGE_SHIFT);
+ goto verify;
+ }
+
+ pmdp = pmd_offset(pudp, addr);
+ if (!pmd_present(*pmdp))
+ goto out;
+
+ if (unlikely(pmd_large(*pmdp))) {
+ pte = *(pte_t *)pmdp;
+ offset = ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+ goto verify;
+ }
+
+ ptep = pte_offset_map(pmdp, addr);
+ pte = gup_get_pte(ptep);
+ pte_unmap(ptep);
+
+verify:
+ if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask)
+ goto out;
+
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+
+ head = pte_page(pte);
+ page = head + offset;
+ VM_BUG_ON(compound_head(page) != head);
+ get_page(page);
+ *writable = !!(pte_flags(pte) & _PAGE_RW);
+
+out:
+ local_irq_restore(flags);
+ return page;
+}
+EXPORT_SYMBOL_GPL(get_user_page_and_protection);
+
--
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Prev: [PATCH 3/6] kvm: rename gfn_to_pfn() etc.
Next: Crypto Fixes for 2.6.35