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Date:	Tue, 8 Feb 2011 14:03:38 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Jan Beulich <JBeulich@...ell.com>
Subject: Re: [PATCH] x86/mm/init: respect memblock reserved regions when
 destroying mappings

On Tue, 8 Feb 2011, Yinghai Lu wrote:
> On Mon, Feb 7, 2011 at 11:00 AM, Stefano Stabellini
> <stefano.stabellini@...citrix.com> wrote:
> > On Mon, 7 Feb 2011, Stefano Stabellini wrote:
> >> On Sun, 6 Feb 2011, Yinghai Lu wrote:
> >> > On 02/05/2011 11:30 PM, H. Peter Anvin wrote:
> >> > > On 02/05/2011 11:02 PM, Yinghai Lu wrote:
> >> > >> why not just move calling cleanup_highmap down?
> >> > >>
> >> > >> something like attached patch.
> >> > >
> >> > > This patch looks very clean and looks on the surface of it like it is
> >> > > removing some ugly ad hoc code, but (as always) it needs a description
> >> > > about the problem it solves and why it is correct.
> >> >
> >> > Sure.
> >> >
> >> >
> >> > Jeremy and xen guys, can you please check if it works well with xen ?
> >> >
> >>
> >> Actually this patch makes things worse on xen, because before
> >> cleanup_highmap() wasn't called at all on xen (on purpose) and now it
> >> is, fully destroying all the mappings we have at _end.
> >>
> >> Can we add a check on memblock reserved regions in cleanup_highmap()?
> >
> > In case you are wondering how Yinghai Lu's patch would look like with
> > the added check, here it is:
> >
> >
> > diff --git a/arch/x86/include/asm/memblock.h b/arch/x86/include/asm/memblock.h
> > index 19ae14b..184f778 100644
> > --- a/arch/x86/include/asm/memblock.h
> > +++ b/arch/x86/include/asm/memblock.h
> > @@ -3,6 +3,7 @@
> >
> >  #define ARCH_DISCARD_MEMBLOCK
> >
> > +bool memblock_check_reserved_size(u64 *addrp, u64 *sizep, u64 align);
> >  u64 memblock_x86_find_in_range_size(u64 start, u64 *sizep, u64 align);
> >  void memblock_x86_to_bootmem(u64 start, u64 end);
> >
> > diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
> > index 975f709..28686b6 100644
> > --- a/arch/x86/include/asm/pgtable_64.h
> > +++ b/arch/x86/include/asm/pgtable_64.h
> > @@ -165,7 +165,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; }
> >  #define __swp_entry_to_pte(x)          ((pte_t) { .pte = (x).val })
> >
> >  extern int kern_addr_valid(unsigned long addr);
> > -extern void cleanup_highmap(void);
> > +extern void cleanup_highmap(unsigned long end);
> >
> >  #define HAVE_ARCH_UNMAPPED_AREA
> >  #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
> > diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> > index 2d2673c..5655c22 100644
> > --- a/arch/x86/kernel/head64.c
> > +++ b/arch/x86/kernel/head64.c
> > @@ -77,9 +77,6 @@ void __init x86_64_start_kernel(char * real_mode_data)
> >        /* Make NULL pointers segfault */
> >        zap_identity_mappings();
> >
> > -       /* Cleanup the over mapped high alias */
> > -       cleanup_highmap();
> > -
> >        max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
> >
> >        for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
> > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> > index d3cfe26..91afde6 100644
> > --- a/arch/x86/kernel/setup.c
> > +++ b/arch/x86/kernel/setup.c
> > @@ -297,6 +297,9 @@ static void __init init_gbpages(void)
> >  static inline void init_gbpages(void)
> >  {
> >  }
> > +static void __init cleanup_highmap(unsigned long end)
> > +{
> > +}
> >  #endif
> >
> >  static void __init reserve_brk(void)
> > @@ -922,6 +925,9 @@ void __init setup_arch(char **cmdline_p)
> >         */
> >        reserve_brk();
> >
> > +       /* Cleanup the over mapped high alias after _brk_end*/
> > +       cleanup_highmap(_brk_end);
> > +
> >        memblock.current_limit = get_max_mapped();
> >        memblock_x86_fill();
> >
> > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> > index 947f42a..f13ff3a 100644
> > --- a/arch/x86/mm/init.c
> > +++ b/arch/x86/mm/init.c
> > @@ -279,25 +279,6 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
> >        load_cr3(swapper_pg_dir);
> >  #endif
> >
> > -#ifdef CONFIG_X86_64
> > -       if (!after_bootmem && !start) {
> > -               pud_t *pud;
> > -               pmd_t *pmd;
> > -
> > -               mmu_cr4_features = read_cr4();
> > -
> > -               /*
> > -                * _brk_end cannot change anymore, but it and _end may be
> > -                * located on different 2M pages. cleanup_highmap(), however,
> > -                * can only consider _end when it runs, so destroy any
> > -                * mappings beyond _brk_end here.
> > -                */
> > -               pud = pud_offset(pgd_offset_k(_brk_end), _brk_end);
> > -               pmd = pmd_offset(pud, _brk_end - 1);
> > -               while (++pmd <= pmd_offset(pud, (unsigned long)_end - 1))
> > -                       pmd_clear(pmd);
> > -       }
> > -#endif
> >        __flush_tlb_all();
> >
> >        if (!after_bootmem && e820_table_end > e820_table_start)
> > diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> > index 71a5929..028c49e 100644
> > --- a/arch/x86/mm/init_64.c
> > +++ b/arch/x86/mm/init_64.c
> > @@ -297,18 +297,26 @@ void __init init_extra_mapping_uc(unsigned long phys, unsigned long size)
> >  * rounded up to the 2MB boundary. This catches the invalid pmds as
> >  * well, as they are located before _text:
> >  */
> > -void __init cleanup_highmap(void)
> > +void __init cleanup_highmap(unsigned long end)
> >  {
> >        unsigned long vaddr = __START_KERNEL_map;
> > -       unsigned long end = roundup((unsigned long)_end, PMD_SIZE) - 1;
> >        pmd_t *pmd = level2_kernel_pgt;
> >        pmd_t *last_pmd = pmd + PTRS_PER_PMD;
> > +       u64 size, addrp;
> > +       bool changed;
> > +
> > +       end = roundup(end, PMD_SIZE) - 1;
> >
> >        for (; pmd < last_pmd; pmd++, vaddr += PMD_SIZE) {
> >                if (pmd_none(*pmd))
> >                        continue;
> > -               if (vaddr < (unsigned long) _text || vaddr > end)
> > -                       set_pmd(pmd, __pmd(0));
> > +               if (vaddr < (unsigned long) _text || vaddr > end) {
> > +                       addrp = __pa(vaddr);
> > +                       size = PMD_SIZE;
> > +                       changed = memblock_check_reserved_size(&addrp, &size, PMD_SIZE);
> > +                       if (!changed && size)
> > +                               set_pmd(pmd, __pmd(0));
> > +               }
> 
> for native path, memblock_check_reserved_size() are called 256 times
> without obvious reasons.


what about this patch, does it look like a reasonable solution?



diff --git a/arch/x86/include/asm/memblock.h b/arch/x86/include/asm/memblock.h
index 19ae14b..184f778 100644
--- a/arch/x86/include/asm/memblock.h
+++ b/arch/x86/include/asm/memblock.h
@@ -3,6 +3,7 @@
 
 #define ARCH_DISCARD_MEMBLOCK
 
+bool memblock_check_reserved_size(u64 *addrp, u64 *sizep, u64 align);
 u64 memblock_x86_find_in_range_size(u64 start, u64 *sizep, u64 align);
 void memblock_x86_to_bootmem(u64 start, u64 end);
 
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 975f709..28686b6 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -165,7 +165,7 @@ static inline int pgd_large(pgd_t pgd) { return 0; }
 #define __swp_entry_to_pte(x)		((pte_t) { .pte = (x).val })
 
 extern int kern_addr_valid(unsigned long addr);
-extern void cleanup_highmap(void);
+extern void cleanup_highmap(unsigned long end);
 
 #define HAVE_ARCH_UNMAPPED_AREA
 #define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 2d2673c..5655c22 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -77,9 +77,6 @@ void __init x86_64_start_kernel(char * real_mode_data)
 	/* Make NULL pointers segfault */
 	zap_identity_mappings();
 
-	/* Cleanup the over mapped high alias */
-	cleanup_highmap();
-
 	max_pfn_mapped = KERNEL_IMAGE_SIZE >> PAGE_SHIFT;
 
 	for (i = 0; i < NUM_EXCEPTION_VECTORS; i++) {
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index d3cfe26..91afde6 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -297,6 +297,9 @@ static void __init init_gbpages(void)
 static inline void init_gbpages(void)
 {
 }
+static void __init cleanup_highmap(unsigned long end)
+{
+}
 #endif
 
 static void __init reserve_brk(void)
@@ -922,6 +925,9 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	reserve_brk();
 
+	/* Cleanup the over mapped high alias after _brk_end*/
+	cleanup_highmap(_brk_end);
+
 	memblock.current_limit = get_max_mapped();
 	memblock_x86_fill();
 
diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index 947f42a..f13ff3a 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -279,25 +279,6 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 	load_cr3(swapper_pg_dir);
 #endif
 
-#ifdef CONFIG_X86_64
-	if (!after_bootmem && !start) {
-		pud_t *pud;
-		pmd_t *pmd;
-
-		mmu_cr4_features = read_cr4();
-
-		/*
-		 * _brk_end cannot change anymore, but it and _end may be
-		 * located on different 2M pages. cleanup_highmap(), however,
-		 * can only consider _end when it runs, so destroy any
-		 * mappings beyond _brk_end here.
-		 */
-		pud = pud_offset(pgd_offset_k(_brk_end), _brk_end);
-		pmd = pmd_offset(pud, _brk_end - 1);
-		while (++pmd <= pmd_offset(pud, (unsigned long)_end - 1))
-			pmd_clear(pmd);
-	}
-#endif
 	__flush_tlb_all();
 
 	if (!after_bootmem && e820_table_end > e820_table_start)
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 71a5929..90a64de 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -297,12 +297,25 @@ void __init init_extra_mapping_uc(unsigned long phys, unsigned long size)
  * rounded up to the 2MB boundary. This catches the invalid pmds as
  * well, as they are located before _text:
  */
-void __init cleanup_highmap(void)
+void __init cleanup_highmap(unsigned long end)
 {
 	unsigned long vaddr = __START_KERNEL_map;
-	unsigned long end = roundup((unsigned long)_end, PMD_SIZE) - 1;
 	pmd_t *pmd = level2_kernel_pgt;
 	pmd_t *last_pmd = pmd + PTRS_PER_PMD;
+	u64 size, addrp;
+	bool changed;
+
+	end = roundup(end, PMD_SIZE) - 1;
+
+	/* check for reserved regions after end */
+	addrp = __pa(end);
+	size = (PTRS_PER_PMD * PMD_SIZE + vaddr) - end;
+	changed = memblock_check_reserved_size(&addrp, &size, PMD_SIZE);
+	if (changed || !size) {
+		/* reserved regions found, avoid removing mappings after end */
+		pud_t *pud = pud_offset(pgd_offset_k(end), end);
+		last_pmd = pmd_offset(pud, end);
+	}
 
 	for (; pmd < last_pmd; pmd++, vaddr += PMD_SIZE) {
 		if (pmd_none(*pmd))
diff --git a/arch/x86/mm/memblock.c b/arch/x86/mm/memblock.c
index aa11693..fac21d4 100644
--- a/arch/x86/mm/memblock.c
+++ b/arch/x86/mm/memblock.c
@@ -8,7 +8,7 @@
 #include <linux/range.h>
 
 /* Check for already reserved areas */
-static bool __init check_with_memblock_reserved_size(u64 *addrp, u64 *sizep, u64 align)
+bool __init memblock_check_reserved_size(u64 *addrp, u64 *sizep, u64 align)
 {
 	struct memblock_region *r;
 	u64 addr = *addrp, last;
@@ -59,7 +59,7 @@ u64 __init memblock_x86_find_in_range_size(u64 start, u64 *sizep, u64 align)
 		if (addr >= ei_last)
 			continue;
 		*sizep = ei_last - addr;
-		while (check_with_memblock_reserved_size(&addr, sizep, align))
+		while (memblock_check_reserved_size(&addr, sizep, align))
 			;
 
 		if (*sizep)

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