[PATCH] x86/mm: Expand static page table for fixmap space

[PATCH] x86/mm: Expand static page table for fixmap space

[Feng Tang]

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@linutronix.de>
Signed-off-by: Feng Tang <feng.tang@intel.com>
---
 arch/x86/include/asm/fixmap.h     |  3 +++
 arch/x86/include/asm/pgtable_64.h |  3 ++-
 arch/x86/kernel/head_64.S         | 16 ++++++++++++----
 arch/x86/mm/pgtable.c             | 10 ++++++++++
 arch/x86/xen/mmu_pv.c             |  4 +++-
 5 files changed, 30 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..a3618cf 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 +446,20 @@ 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_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..a4052b1 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

Re: [PATCH] x86/mm: Expand static page table for fixmap space

[Juergen Gross]

On 17/09/18 09:34, Feng Tang wrote:
> 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@linutronix.de>
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
>  arch/x86/include/asm/fixmap.h     |  3 +++
>  arch/x86/include/asm/pgtable_64.h |  3 ++-
>  arch/x86/kernel/head_64.S         | 16 ++++++++++++----
>  arch/x86/mm/pgtable.c             | 10 ++++++++++
>  arch/x86/xen/mmu_pv.c             |  4 +++-
>  5 files changed, 30 insertions(+), 6 deletions(-)
> 

...

> 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);

Please use PTRS_PER_PTE instead of the literal 512.

Some lines further up level1_fixmap_pgt is mentioned in a comment.
Please update that, too:

-	/* L3_k[511][506] -> level1_fixmap_pgt */
+	/* L3_k[511][506, ...] -> level1_fixmap_pgt */


Juergen

Re: [PATCH] x86/mm: Expand static page table for fixmap space

[Feng Tang]

Hi Juergen,

On Mon, Sep 17, 2018 at 09:48:05AM +0200, Juergen Gross wrote:
> On 17/09/18 09:34, Feng Tang wrote:
> > 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@linutronix.de>
> > Signed-off-by: Feng Tang <feng.tang@intel.com>
> > ---
> >  arch/x86/include/asm/fixmap.h     |  3 +++
> >  arch/x86/include/asm/pgtable_64.h |  3 ++-
> >  arch/x86/kernel/head_64.S         | 16 ++++++++++++----
> >  arch/x86/mm/pgtable.c             | 10 ++++++++++
> >  arch/x86/xen/mmu_pv.c             |  4 +++-
> >  5 files changed, 30 insertions(+), 6 deletions(-)
> > 
> 
> ...
> 
> > 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);
> 
> Please use PTRS_PER_PTE instead of the literal 512.
> 
> Some lines further up level1_fixmap_pgt is mentioned in a comment.
> Please update that, too:
> 
> -	/* L3_k[511][506] -> level1_fixmap_pgt */
> +	/* L3_k[511][506, ...] -> level1_fixmap_pgt */

Thanks for the suggestions, will handle them in v2.

- Feng

> 
> 
> Juergen