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Date: Mon, 17 Sep 2018 15:01:35 +0800
From: Feng Tang <feng.tang@...el.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Michal Hocko <mhocko@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
Ingo Molnar <mingo@...e.hu>,
"H . Peter Anvin" <hpa@...ux.intel.com>,
Yinghai Lu <yinghai@...nel.org>,
Dave Hansen <dave.hansen@...el.com>,
Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86, mm: Reserver some memory for bootmem allocator for
NO_BOOTMEM
Hi Thomas,
On Sun, Sep 16, 2018 at 11:06:41PM +0800, Feng Tang wrote:
> Hi Thomas,
>
> On Sun, Sep 16, 2018 at 04:43:55PM +0200, Thomas Gleixner wrote:
> > On Sun, 16 Sep 2018, Feng Tang wrote:
> > > diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> > > index e848a4811785..a927f5f39bee 100644
> > > --- a/arch/x86/mm/pgtable.c
> > > +++ b/arch/x86/mm/pgtable.c
> > > @@ -637,6 +637,16 @@ void __native_set_fixmap(enum fixed_addresses idx, pte_t pte)
> > > {
> > > unsigned long address = __fix_to_virt(idx);
> > >
> > > +#ifdef CONFIG_X86_64
> > > + /*
> > > + * In arch/x86/kernel/head_64.S, the static page table has
> > > + * been setup for fixmap. Add a sanity compiling check
> > > + * whether fixmap space has exceeded the capacity.
> > > + */
> > > + BUILD_BUG_ON((__end_of_permanent_fixed_addresses + 511)/512
> > > + > FIXMAP_PMD_NUM);
> >
> > There exist macros for rounding up and doing this in the header file is
> > perfectly fine.
>
> I'll find the sample for the round up.
>
> And for the header file check, I initially put this check directly in
> the fixmap.h like:
>
> #if ((__end_of_permanent_fixed_addresses + 511)/512 > FIXMAP_PMD_NUM)
> #erro "some warning...."
> #endif
>
> But failed to compile, I got the warning
> warning: "__end_of_permanent_fixed_addresses" is not defined
>
> I guess the header file preprocessing can't handle it.
Below is a patch against 4.19-rc4, verified with earlycon
working fine, please review, thanks!
- Feng
---
>From 2710b48eb29a86c8ee568d00d5b04820c3fe1f3a Mon Sep 17 00:00:00 2001
From: Feng Tang <feng.tang@...el.com>
Date: Mon, 17 Sep 2018 12:12:08 +0800
Subject: [PATCH] x86/mm: Expand static page table for fixmap space
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 acutually could be in 4M space
with different kernel configurations.
So increase the static space to 4M for now by defining FIXMAP_PMD_NUM
to 2, and add a build time check for future possible overflow so that
the macro could be increased accordingly.
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Feng Tang <feng.tang@...el.com>
---
arch/x86/include/asm/fixmap.h | 3 +++
arch/x86/include/asm/pgtable_64.h | 3 ++-
arch/x86/kernel/head_64.S | 15 +++++++++++----
arch/x86/mm/pgtable.c | 10 ++++++++++
arch/x86/xen/mmu_pv.c | 4 +++-
5 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index e203169..ffaa0fa 100644
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -14,6 +14,9 @@
#ifndef _ASM_X86_FIXMAP_H
#define _ASM_X86_FIXMAP_H
+/* Put here to be accessble for assembly code like head_64.S */
+#define FIXMAP_PMD_NUM 2
+
#ifndef __ASSEMBLY__
#include <linux/kernel.h>
#include <asm/acpi.h>
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index ce2b590..9c85b54 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -14,6 +14,7 @@
#include <asm/processor.h>
#include <linux/bitops.h>
#include <linux/threads.h>
+#include <asm/fixmap.h>
extern p4d_t level4_kernel_pgt[512];
extern p4d_t level4_ident_pgt[512];
@@ -22,7 +23,7 @@ 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_top_pgt[];
#define swapper_pg_dir init_top_pgt
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 15ebc2f..985eaff 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -24,6 +24,7 @@
#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>
@@ -445,13 +446,19 @@ 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_NOENC
- /* 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_NOENC
+ 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
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index ae39455..c9d94d0 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -637,6 +637,16 @@ void __native_set_fixmap(enum fixed_addresses idx, pte_t pte)
{
unsigned long address = __fix_to_virt(idx);
+#ifdef CONFIG_X86_64
+ /*
+ * In arch/x86/kernel/head_64.S, the static page table has
+ * been setup for fixmap. Add a sanity compiling check
+ * whether fixmap space has exceeded the capacity.
+ */
+ BUILD_BUG_ON(__end_of_permanent_fixed_addresses
+ > (FIXMAP_PMD_NUM * PTRS_PER_PMD));
+#endif
+
if (idx >= __end_of_fixed_addresses) {
BUG();
return;
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 2fe5c9b..19077f9 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -1952,7 +1952,9 @@ void __init xen_setup_kernel_pagetable(pgd_t *pgd, unsigned long max_pfn)
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 * 512, PAGE_KERNEL_RO);
/* Pin down new L4 */
pin_pagetable_pfn(MMUEXT_PIN_L4_TABLE,
--
2.7.4
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