From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Subject: [PATCH 04/11] xen/mmu: Provide comments describing the _ka and _va aliasing issue
Date: Thu, 16 Aug 2012 12:03:22 -0400 [thread overview]
Message-ID: <1345133009-21941-5-git-send-email-konrad.wilk@oracle.com> (raw)
In-Reply-To: <1345133009-21941-1-git-send-email-konrad.wilk@oracle.com>
Which is that the level2_kernel_pgt (__ka virtual addresses)
and level2_ident_pgt (__va virtual address) contain the same
PMD entries. So if you modify a PTE in __ka, it will be reflected
in __va (and vice-versa).
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
arch/x86/xen/mmu.c | 17 +++++++++++++++++
1 files changed, 17 insertions(+), 0 deletions(-)
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 4ac21a4..6ba6100 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -1734,19 +1734,36 @@ 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 __ka space! (But if you just
+ * modify the PMD table to point to other PTE's or none, then you
+ * are OK - which is what cleanup_highmap does) */
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
next prev parent reply other threads:[~2012-08-16 16:16 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-16 16:03 [PATCH] Boot PV guests with more than 128GB (v3) for v3.7 Konrad Rzeszutek Wilk
2012-08-16 16:03 ` [PATCH 01/11] xen/p2m: Fix the comment describing the P2M tree Konrad Rzeszutek Wilk
2012-08-17 17:29 ` [Xen-devel] " Stefano Stabellini
2012-08-16 16:03 ` [PATCH 02/11] xen/x86: Use memblock_reserve for sensitive areas Konrad Rzeszutek Wilk
2012-08-17 17:35 ` [Xen-devel] " Stefano Stabellini
2012-08-20 14:13 ` Konrad Rzeszutek Wilk
2012-08-21 17:27 ` Q:pt_base in COMPAT mode offset by two pages. Was:Re: " Konrad Rzeszutek Wilk
2012-08-21 19:03 ` Konrad Rzeszutek Wilk
2012-08-22 10:48 ` Stefano Stabellini
2012-08-22 14:00 ` Konrad Rzeszutek Wilk
2012-08-22 14:12 ` Jan Beulich
2012-08-22 14:41 ` Stefano Stabellini
2012-08-22 14:57 ` Konrad Rzeszutek Wilk
2012-08-22 15:59 ` Jan Beulich
2012-08-22 16:21 ` Konrad Rzeszutek Wilk
2012-08-22 18:55 ` [Xen-devel] Q:pt_base in COMPAT mode offset by two pages. Was:Re: " Konrad Rzeszutek Wilk
2012-08-23 6:23 ` Jan Beulich
2012-08-16 16:03 ` [PATCH 03/11] xen/mmu: The xen_setup_kernel_pagetable doesn't need to return anything Konrad Rzeszutek Wilk
2012-08-16 16:03 ` Konrad Rzeszutek Wilk [this message]
2012-08-16 16:03 ` [PATCH 05/11] xen/mmu: use copy_page instead of memcpy Konrad Rzeszutek Wilk
2012-08-16 16:03 ` [PATCH 06/11] xen/mmu: For 64-bit do not call xen_map_identity_early Konrad Rzeszutek Wilk
2012-08-17 17:41 ` [Xen-devel] " Stefano Stabellini
2012-08-17 17:45 ` Konrad Rzeszutek Wilk
2012-08-20 11:45 ` Stefano Stabellini
2012-08-20 11:53 ` Ian Campbell
2012-08-20 11:58 ` Stefano Stabellini
2012-08-20 12:06 ` Konrad Rzeszutek Wilk
2012-08-20 12:19 ` Stefano Stabellini
2012-08-23 15:40 ` Konrad Rzeszutek Wilk
2012-08-23 15:57 ` Stefano Stabellini
2012-08-16 16:03 ` [PATCH 07/11] xen/mmu: Recycle the Xen provided L4, L3, and L2 pages Konrad Rzeszutek Wilk
2012-08-17 18:07 ` [Xen-devel] " Stefano Stabellini
2012-08-17 18:05 ` Konrad Rzeszutek Wilk
2012-08-16 16:03 ` [PATCH 08/11] xen/p2m: Add logic to revector a P2M tree to use __va leafs Konrad Rzeszutek Wilk
2012-08-16 16:03 ` [PATCH 09/11] xen/mmu: Copy and revector the P2M tree Konrad Rzeszutek Wilk
2012-08-16 16:03 ` [PATCH 10/11] xen/mmu: Remove from __ka space PMD entries for pagetables Konrad Rzeszutek Wilk
2012-08-16 16:03 ` [PATCH 11/11] xen/mmu: Release just the MFN list, not MFN list and part of pagetables Konrad Rzeszutek Wilk
2012-08-21 14:18 ` [Xen-devel] " Stefano Stabellini
2012-08-21 14:57 ` Konrad Rzeszutek Wilk
2012-08-21 15:27 ` Stefano Stabellini
2012-09-17 18:06 ` William Dauchy
2012-09-17 18:18 ` Konrad Rzeszutek Wilk
2012-08-17 17:39 ` [PATCH] Boot PV guests with more than 128GB (v3) for v3.7 Konrad Rzeszutek Wilk
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