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SubjectRe: [PATCH 4.9 23/35] x86/mm: Expand static page table for fixmap space
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On Thu, 2018-10-11 at 17:35 +0200, Greg Kroah-Hartman wrote:
> 4.9-stable review patch. If anyone has any objections, please let me know.
>
> ------------------
>
> From: Feng Tang <feng.tang@intel.com>
>
> commit 05ab1d8a4b36ee912b7087c6da127439ed0a903e upstream.

This backport is incorrect. The part that updated __startup_64() in
arch/x86/kernel/head64.c was dropped, presumably because that function
doesn't exist in 4.9. However that seems to be an essential of the
fix. In 4.9 the startup_64 routine in arch/x86/kernel/head_64.S would
need to be changed instead.

I also found that this introduces new boot-time warnings on some
systems if CONFIG_DEBUG_WX is enabled.

So, unless someone provides fixes for those issues, I think this should
be reverted for the 4.9 branch.

Ben.

> We met a kernel panic when enabling earlycon, which is due to the fixmap
> address of earlycon is not statically setup.
>
> Currently the static fixmap setup in head_64.S only covers 2M virtual
> address space, while it actually could be in 4M space with different
> kernel configurations, e.g. when VSYSCALL emulation is disabled.
>
> So increase the static space to 4M for now by defining FIXMAP_PMD_NUM to 2,
> and add a build time check to ensure that the fixmap is covered by the
> initial static page tables.
>
> Fixes: 1ad83c858c7d ("x86_64,vsyscall: Make vsyscall emulation configurable")
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Tested-by: kernel test robot <rong.a.chen@intel.com>
> Reviewed-by: Juergen Gross <jgross@suse.com> (Xen parts)
> Cc: H Peter Anvin <hpa@linux.intel.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Yinghai Lu <yinghai@kernel.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Andy Lutomirsky <luto@kernel.org>
> Cc: stable@vger.kernel.org
> Link: https://lkml.kernel.org/r/20180920025828.23699-1-feng.tang@intel.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> arch/x86/include/asm/fixmap.h | 10 ++++++++++
> arch/x86/include/asm/pgtable_64.h | 3 ++-
> arch/x86/kernel/head_64.S | 16 ++++++++++++----
> arch/x86/mm/pgtable.c | 9 +++++++++
> arch/x86/xen/mmu.c | 8 ++++++--
> 5 files changed, 39 insertions(+), 7 deletions(-)
>
> --- a/arch/x86/include/asm/fixmap.h
> +++ b/arch/x86/include/asm/fixmap.h
> @@ -14,6 +14,16 @@
> #ifndef _ASM_X86_FIXMAP_H
> #define _ASM_X86_FIXMAP_H
>
> +/*
> + * Exposed to assembly code for setting up initial page tables. Cannot be
> + * calculated in assembly code (fixmap entries are an enum), but is sanity
> + * checked in the actual fixmap C code to make sure that the fixmap is
> + * covered fully.
> + */
> +#define FIXMAP_PMD_NUM 2
> +/* fixmap starts downwards from the 507th entry in level2_fixmap_pgt */
> +#define FIXMAP_PMD_TOP 507
> +
> #ifndef __ASSEMBLY__
> #include <linux/kernel.h>
> #include <asm/acpi.h>
> --- a/arch/x86/include/asm/pgtable_64.h
> +++ b/arch/x86/include/asm/pgtable_64.h
> @@ -13,13 +13,14 @@
> #include <asm/processor.h>
> #include <linux/bitops.h>
> #include <linux/threads.h>
> +#include <asm/fixmap.h>
>
> extern pud_t level3_kernel_pgt[512];
> extern pud_t level3_ident_pgt[512];
> extern pmd_t level2_kernel_pgt[512];
> extern pmd_t level2_fixmap_pgt[512];
> extern pmd_t level2_ident_pgt[512];
> -extern pte_t level1_fixmap_pgt[512];
> +extern pte_t level1_fixmap_pgt[512 * FIXMAP_PMD_NUM];
> extern pgd_t init_level4_pgt[];
>
> #define swapper_pg_dir init_level4_pgt
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -23,6 +23,7 @@
> #include "../entry/calling.h"
> #include <asm/export.h>
> #include <asm/nospec-branch.h>
> +#include <asm/fixmap.h>
>
> #ifdef CONFIG_PARAVIRT
> #include <asm/asm-offsets.h>
> @@ -493,13 +494,20 @@ NEXT_PAGE(level2_kernel_pgt)
> KERNEL_IMAGE_SIZE/PMD_SIZE)
>
> NEXT_PAGE(level2_fixmap_pgt)
> - .fill 506,8,0
> - .quad level1_fixmap_pgt - __START_KERNEL_map + _PAGE_TABLE
> - /* 8MB reserved for vsyscalls + a 2MB hole = 4 + 1 entries */
> - .fill 5,8,0
> + .fill (512 - 4 - FIXMAP_PMD_NUM),8,0
> + pgtno = 0
> + .rept (FIXMAP_PMD_NUM)
> + .quad level1_fixmap_pgt + (pgtno << PAGE_SHIFT) - __START_KERNEL_map \
> + + _PAGE_TABLE;
> + pgtno = pgtno + 1
> + .endr
> + /* 6 MB reserved space + a 2MB hole */
> + .fill 4,8,0
>
> NEXT_PAGE(level1_fixmap_pgt)
> + .rept (FIXMAP_PMD_NUM)
> .fill 512,8,0
> + .endr
>
> #undef PMDS
>
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -536,6 +536,15 @@ void __native_set_fixmap(enum fixed_addr
> {
> unsigned long address = __fix_to_virt(idx);
>
> +#ifdef CONFIG_X86_64
> + /*
> + * Ensure that the static initial page tables are covering the
> + * fixmap completely.
> + */
> + BUILD_BUG_ON(__end_of_permanent_fixed_addresses >
> + (FIXMAP_PMD_NUM * PTRS_PER_PTE));
> +#endif
> +
> if (idx >= __end_of_fixed_addresses) {
> BUG();
> return;
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -1936,7 +1936,7 @@ void __init xen_setup_kernel_pagetable(p
> * L3_k[511] -> level2_fixmap_pgt */
> convert_pfn_mfn(level3_kernel_pgt);
>
> - /* L3_k[511][506] -> level1_fixmap_pgt */
> + /* L3_k[511][508-FIXMAP_PMD_NUM ... 507] -> level1_fixmap_pgt */
> convert_pfn_mfn(level2_fixmap_pgt);
> }
> /* We get [511][511] and have Xen's version of level2_kernel_pgt */
> @@ -1970,7 +1970,11 @@ void __init xen_setup_kernel_pagetable(p
> set_page_prot(level2_ident_pgt, PAGE_KERNEL_RO);
> set_page_prot(level2_kernel_pgt, PAGE_KERNEL_RO);
> set_page_prot(level2_fixmap_pgt, PAGE_KERNEL_RO);
> - set_page_prot(level1_fixmap_pgt, PAGE_KERNEL_RO);
> +
> + for (i = 0; i < FIXMAP_PMD_NUM; i++) {
> + set_page_prot(level1_fixmap_pgt + i * PTRS_PER_PTE,
> + PAGE_KERNEL_RO);
> + }
>
> /* Pin down new L4 */
> pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE,
>
>
--
Ben Hutchings
Absolutum obsoletum. (If it works, it's out of date.) - Stafford Beer


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