[Xen-devel] [PATCH] espfix/xen: Fix allocation of pages for paravirt page tables

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

init_espfix_ap() is currently off by one level when informing hypervisor
that allocated pages will be used for ministacks' page tables.

The most immediate effect of this on a PV guest is that if
'stack_page = __get_free_page()' returns a non-zeroed-out page the hypervisor
will refuse to use it for a page table (which it shouldn't be anyway). This will
result in warnings by both Xen and Linux.

More importantly, a subsequent write to that page (again, by a PV guest) is
likely to result in fatal page fault.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 arch/x86/kernel/espfix_64.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 6afbb16..94d857f 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -175,7 +175,7 @@ void init_espfix_ap(void)
        if (!pud_present(pud)) {
                pmd_p = (pmd_t *)__get_free_page(PGALLOC_GFP);
                pud = __pud(__pa(pmd_p) | (PGTABLE_PROT & ptemask));
-               paravirt_alloc_pud(&init_mm, __pa(pmd_p) >> PAGE_SHIFT);
+               paravirt_alloc_pmd(&init_mm, __pa(pmd_p) >> PAGE_SHIFT);
                for (n = 0; n < ESPFIX_PUD_CLONES; n++)
                        set_pud(&pud_p[n], pud);
        }
@@ -185,7 +185,7 @@ void init_espfix_ap(void)
        if (!pmd_present(pmd)) {
                pte_p = (pte_t *)__get_free_page(PGALLOC_GFP);
                pmd = __pmd(__pa(pte_p) | (PGTABLE_PROT & ptemask));
-               paravirt_alloc_pmd(&init_mm, __pa(pte_p) >> PAGE_SHIFT);
+               paravirt_alloc_pte(&init_mm, __pa(pte_p) >> PAGE_SHIFT);
                for (n = 0; n < ESPFIX_PMD_CLONES; n++)
                        set_pmd(&pmd_p[n], pmd);
        }
@@ -193,7 +193,6 @@ void init_espfix_ap(void)
        pte_p = pte_offset_kernel(&pmd, addr);
        stack_page = (void *)__get_free_page(GFP_KERNEL);
        pte = __pte(__pa(stack_page) | (__PAGE_KERNEL_RO & ptemask));
-       paravirt_alloc_pte(&init_mm, __pa(stack_page) >> PAGE_SHIFT);
        for (n = 0; n < ESPFIX_PTE_CLONES; n++)
                set_pte(&pte_p[n*PTE_STRIDE], pte);
 
-- 
1.8.1.4


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