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Message-Id: <1343068103-13579-4-git-send-email-konrad.wilk@oracle.com> Date: Mon, 23 Jul 2012 14:28:21 -0400 From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> To: linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com> Subject: [PATCH 3/5] xen/mmu: Provide comments describing the _kva and _va aliasing issue And also explain how the pagetables are being grafted on. Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.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 4ac21a4..b0b72e0 100644 --- a/arch/x86/xen/mmu.c +++ b/arch/x86/xen/mmu.c @@ -1734,19 +1734,34 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn) init_level4_pgt[0] = __pgd(0); /* Pre-constructed entries are in pfn, so convert to mfn */ + /* L4[272] -> level3_ident_pgt + * L4[511] -> level3_kernel_pgt */ convert_pfn_mfn(init_level4_pgt); + + /* L3_i[0] -> level2_ident_pgt */ convert_pfn_mfn(level3_ident_pgt); + /* L3_k[510] -> level2_kernel_pgt + * L3_i[511] -> level2_fixmap_pgt */ convert_pfn_mfn(level3_kernel_pgt); + /* We get [511][511] and have Xen's version of level2_kernel_pgt */ l3 = m2v(pgd[pgd_index(__START_KERNEL_map)].pgd); l2 = m2v(l3[pud_index(__START_KERNEL_map)].pud); + /* Graft it onto L4[272][0]. Note that we creating an aliasing problem: + * Both L4[272][0] and L4[511][511] have entries that point to the same + * L2 (PMD) tables. Meaning that if you modify it in __va space + * it will be also modified in the __kva space! */ memcpy(level2_ident_pgt, l2, sizeof(pmd_t) * PTRS_PER_PMD); + /* Graft it onto L4[511][511] */ memcpy(level2_kernel_pgt, l2, sizeof(pmd_t) * PTRS_PER_PMD); + /* Get [511][510] and graft that in level2_fixmap_pgt */ l3 = m2v(pgd[pgd_index(__START_KERNEL_map + PMD_SIZE)].pgd); l2 = m2v(l3[pud_index(__START_KERNEL_map + PMD_SIZE)].pud); memcpy(level2_fixmap_pgt, l2, sizeof(pmd_t) * PTRS_PER_PMD); + /* Note that we don't do anything with level1_fixmap_pgt which + * we don't need. */ /* Set up identity map */ xen_map_identity_early(level2_ident_pgt, max_pfn); -- 1.7.7.6 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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