Jeremy Fitzhardinge
2009-Mar-23 18:09 UTC
[Xen-devel] [PATCH 10/15] xen: clear reserved bits in l3 entries given in the initial pagetables
From: Ian Campbell <ian.campbell@citrix.com> Impact: workaround Xen bug in 32-on-64 dom0 In native PAE, the only flag that may be legitimately set in an L3 entry is Present. When Xen grafts the top-level PAE L3 pagetable entries into the L4 pagetable, it must also set the other permissions flags so that the mapped pages are actually accessible. However, due to a bug in the hypervisor, it validates update to the L3 entries as formal PAE entries, so it will refuse to validate these entries with the extra bits requires for 4-level pagetables. This patch simply masks the entries back to the bare PAE level, leaving Xen to add whatever bits it feels are necessary. Signed-off-by: Ian Campbell <ian.campbell@citrix.com> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> --- arch/x86/xen/mmu.c | 15 +++++++++++++++ 1 files changed, 15 insertions(+), 0 deletions(-) diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c index 2834852..463a819 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -1855,6 +1855,7 @@ __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) { pmd_t *kernel_pmd; + int i; max_pfn_mapped = PFN_DOWN(__pa(xen_start_info->pt_base) + xen_start_info->nr_pt_frames * PAGE_SIZE + @@ -1866,6 +1867,20 @@ __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd, xen_map_identity_early(level2_kernel_pgt, max_pfn); memcpy(swapper_pg_dir, pgd, sizeof(pgd_t) * PTRS_PER_PGD); + + /* + * When running a 32 bit domain 0 on a 64 bit hypervisor a + * pinned L3 (such as the initial pgd here) contains bits + * which are reserved in the PAE layout but not in the 64 bit + * layout. Unfortunately some versions of the hypervisor + * (incorrectly) validate compat mode guests against the PAE + * layout and hence will not allow such a pagetable to be + * pinned by the guest. Therefore we mask off only the PFN and + * Present bits of the supplied L3. + */ + for (i = 0; i < PTRS_PER_PGD; i++) + swapper_pg_dir[i].pgd &= (PTE_PFN_MASK | _PAGE_PRESENT); + set_pgd(&swapper_pg_dir[KERNEL_PGD_BOUNDARY], __pgd(__pa(level2_kernel_pgt) | _PAGE_PRESENT)); -- 1.6.0.6 _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel