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Message-ID: <1290628896.3144.9.camel@cthulhu.hellion.org.uk>
Date: Wed, 24 Nov 2010 20:01:36 +0000
From: Ian Campbell <Ian.Campbell@...rix.com>
To: Jeremy Fitzhardinge <jeremy@...p.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH] xen: x86/32: perform initial startup on
initial_page_table
On Wed, 2010-11-24 at 18:19 +0000, Jeremy Fitzhardinge wrote:
> On 11/24/2010 04:09 AM, Ian Campbell wrote:
> > Only make swapper_pg_dir readonly and pinned when generic x86 architecture code
> > (which also starts on initial_page_table) switches to it. This helps ensure
> > that the generic setup paths work on Xen unmodified. In particular
> > clone_pgd_range writes directly to the destination pgd entries and is used to
> > initialise swapper_pg_dir so we need to ensure that it remains writeable until
> > the last possible moment during bring up.
> >
> > This is complicated slightly by the need to avoid sharing kernel PMD entries
> > when running under Xen, therefore the Xen implementation must make a copy of
> > the kernel PMD (which is otherwise referred to by both intial_page_table and
> > swapper_pg_dir) before switching to swapper_pg_dir.
>
> The one thing I'd add is the commit ID of the change which made this
> necessary.
Yes, I thought I had but didn't guilt refresh the patch so it didn't
show up.
8<------------------
>From 18ccc13b574dd0d5eb61398ea0da8999638e0d67 Mon Sep 17 00:00:00 2001
From: Ian Campbell <ian.campbell@...rix.com>
Date: Wed, 24 Nov 2010 09:14:51 +0000
Subject: [PATCH] xen: x86/32: perform initial startup on initial_page_table
Only make swapper_pg_dir readonly and pinned when generic x86
architecture code (which, since b40827fa7268, also initially starts on
initial_page_table) switches to it.
This helps ensure that the generic setup paths work on Xen
unmodified. In particular clone_pgd_range writes directly to the
destination pgd entries and is used to initialise swapper_pg_dir so we
need to ensure that it remains writeable until the last possible
moment during bring up.
This is complicated slightly by the need to avoid sharing kernel PMD entries
when running under Xen, therefore the Xen implementation must make a copy of
the kernel PMD (which is otherwise referred to by both intial_page_table and
swapper_pg_dir) before switching to swapper_pg_dir.
Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...ux.intel.com>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
---
arch/x86/xen/enlighten.c | 2 -
arch/x86/xen/mmu.c | 69 +++++++++++++++++++++++++++++++++++++--------
2 files changed, 56 insertions(+), 15 deletions(-)
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 7250bef..02c710b 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1200,8 +1200,6 @@ asmlinkage void __init xen_start_kernel(void)
/* Allocate and initialize top and mid mfn levels for p2m structure */
xen_build_mfn_list_list();
- init_mm.pgd = pgd;
-
/* keep using Xen gdt for now; no urgent need to change it */
#ifdef CONFIG_X86_32
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 790af90..a1feff9 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -2133,44 +2133,83 @@ __init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd,
return pgd;
}
#else /* !CONFIG_X86_64 */
-static RESERVE_BRK_ARRAY(pmd_t, level2_kernel_pgt, PTRS_PER_PMD);
+static RESERVE_BRK_ARRAY(pmd_t, initial_kernel_pmd, PTRS_PER_PMD);
+static RESERVE_BRK_ARRAY(pmd_t, swapper_kernel_pmd, PTRS_PER_PMD);
+
+static __init void xen_write_cr3_init(unsigned long cr3)
+{
+ unsigned long pfn = PFN_DOWN(__pa(swapper_pg_dir));
+
+ BUG_ON(read_cr3() != __pa(initial_page_table));
+ BUG_ON(cr3 != __pa(swapper_pg_dir));
+
+ /*
+ * We are switching to swapper_pg_dir for the first time (from
+ * initial_page_table) and therefore need to mark that page
+ * read-only and then pin it.
+ *
+ * Xen disallows sharing of kernel PMDs for PAE
+ * guests. Therefore we must copy the kernel PMD from
+ * initial_page_table into a new kernel PMD to be used in
+ * swapper_pg_dir.
+ */
+ swapper_kernel_pmd =
+ extend_brk(sizeof(pmd_t) * PTRS_PER_PMD, PAGE_SIZE);
+ memcpy(swapper_kernel_pmd, initial_kernel_pmd,
+ sizeof(pmd_t) * PTRS_PER_PMD);
+ swapper_pg_dir[KERNEL_PGD_BOUNDARY] =
+ __pgd(__pa(swapper_kernel_pmd) | _PAGE_PRESENT);
+ set_page_prot(swapper_kernel_pmd, PAGE_KERNEL_RO);
+
+ set_page_prot(swapper_pg_dir, PAGE_KERNEL_RO);
+ xen_write_cr3(cr3);
+ pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, pfn);
+
+ pin_pagetable_pfn(MMUEXT_UNPIN_TABLE,
+ PFN_DOWN(__pa(initial_page_table)));
+ set_page_prot(initial_page_table, PAGE_KERNEL);
+ set_page_prot(initial_kernel_pmd, PAGE_KERNEL);
+
+ pv_mmu_ops.write_cr3 = &xen_write_cr3;
+}
__init pgd_t *xen_setup_kernel_pagetable(pgd_t *pgd,
unsigned long max_pfn)
{
pmd_t *kernel_pmd;
- level2_kernel_pgt = extend_brk(sizeof(pmd_t) * PTRS_PER_PMD, PAGE_SIZE);
+ initial_kernel_pmd =
+ extend_brk(sizeof(pmd_t) * PTRS_PER_PMD, PAGE_SIZE);
max_pfn_mapped = PFN_DOWN(__pa(xen_start_info->pt_base) +
xen_start_info->nr_pt_frames * PAGE_SIZE +
512*1024);
kernel_pmd = m2v(pgd[KERNEL_PGD_BOUNDARY].pgd);
- memcpy(level2_kernel_pgt, kernel_pmd, sizeof(pmd_t) * PTRS_PER_PMD);
+ memcpy(initial_kernel_pmd, kernel_pmd, sizeof(pmd_t) * PTRS_PER_PMD);
- xen_map_identity_early(level2_kernel_pgt, max_pfn);
+ xen_map_identity_early(initial_kernel_pmd, max_pfn);
- memcpy(swapper_pg_dir, pgd, sizeof(pgd_t) * PTRS_PER_PGD);
- set_pgd(&swapper_pg_dir[KERNEL_PGD_BOUNDARY],
- __pgd(__pa(level2_kernel_pgt) | _PAGE_PRESENT));
+ memcpy(initial_page_table, pgd, sizeof(pgd_t) * PTRS_PER_PGD);
+ initial_page_table[KERNEL_PGD_BOUNDARY] =
+ __pgd(__pa(initial_kernel_pmd) | _PAGE_PRESENT);
- set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
- set_page_prot(swapper_pg_dir, PAGE_KERNEL_RO);
+ set_page_prot(initial_kernel_pmd, PAGE_KERNEL_RO);
+ set_page_prot(initial_page_table, PAGE_KERNEL_RO);
set_page_prot(empty_zero_page, PAGE_KERNEL_RO);
pin_pagetable_pfn(MMUEXT_UNPIN_TABLE, PFN_DOWN(__pa(pgd)));
- xen_write_cr3(__pa(swapper_pg_dir));
-
- pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE, PFN_DOWN(__pa(swapper_pg_dir)));
+ pin_pagetable_pfn(MMUEXT_PIN_L3_TABLE,
+ PFN_DOWN(__pa(initial_page_table)));
+ xen_write_cr3(__pa(initial_page_table));
memblock_x86_reserve_range(__pa(xen_start_info->pt_base),
__pa(xen_start_info->pt_base +
xen_start_info->nr_pt_frames * PAGE_SIZE),
"XEN PAGETABLES");
- return swapper_pg_dir;
+ return initial_page_table;
}
#endif /* CONFIG_X86_64 */
@@ -2304,7 +2343,11 @@ static const struct pv_mmu_ops xen_mmu_ops __initdata = {
.write_cr2 = xen_write_cr2,
.read_cr3 = xen_read_cr3,
+#ifdef CONFIG_X86_32
+ .write_cr3 = xen_write_cr3_init,
+#else
.write_cr3 = xen_write_cr3,
+#endif
.flush_tlb_user = xen_flush_tlb,
.flush_tlb_kernel = xen_flush_tlb,
--
1.5.6.5
--
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