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Date: Fri, 24 Aug 2012 18:07:01 -0700
From: Yinghai Lu <yinghai@...nel.org>
To: Jacob Shin <jacob.shin@....com>
Cc: X86-ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
"H. Peter Anvin" <hpa@...or.com>, Tejun Heo <tj@...nel.org>,
Dave Young <dyoung@...hat.com>,
Chao Wang <chaowang@...hat.com>,
Vivek Goyal <vgoyal@...hat.com>,
Andreas Herrmann <andreas.herrmann3@....com>,
Borislav Petkov <borislav.petkov@....com>
Subject: Re: [PATCH 3/5] x86: Only direct map addresses that are marked as E820_RAM
On Fri, Aug 24, 2012 at 4:55 PM, Jacob Shin <jacob.shin@....com> wrote:
> Currently direct mappings are created for [ 0 to max_low_pfn<<PAGE_SHIFT )
> and [ 4GB to max_pfn<<PAGE_SHIFT ), which may include regions that are not
> backed by actual DRAM. This is fine for holes under 4GB which are covered
> by fixed and variable range MTRRs to be UC. However, we run into trouble
> on higher memory addresses which cannot be covered by MTRRs.
>
> Our system with 1TB of RAM has an e820 that looks like this:
>
> BIOS-e820: [mem 0x0000000000000000-0x00000000000983ff] usable
> BIOS-e820: [mem 0x0000000000098400-0x000000000009ffff] reserved
> BIOS-e820: [mem 0x00000000000d0000-0x00000000000fffff] reserved
> BIOS-e820: [mem 0x0000000000100000-0x00000000c7ebffff] usable
> BIOS-e820: [mem 0x00000000c7ec0000-0x00000000c7ed7fff] ACPI data
> BIOS-e820: [mem 0x00000000c7ed8000-0x00000000c7ed9fff] ACPI NVS
> BIOS-e820: [mem 0x00000000c7eda000-0x00000000c7ffffff] reserved
> BIOS-e820: [mem 0x00000000fec00000-0x00000000fec0ffff] reserved
> BIOS-e820: [mem 0x00000000fee00000-0x00000000fee00fff] reserved
> BIOS-e820: [mem 0x00000000fff00000-0x00000000ffffffff] reserved
> BIOS-e820: [mem 0x0000000100000000-0x000000e037ffffff] usable
> BIOS-e820: [mem 0x000000e038000000-0x000000fcffffffff] reserved
> BIOS-e820: [mem 0x0000010000000000-0x0000011ffeffffff] usable
>
> and so direct mappings are created for huge memory hole between
> 0x000000e038000000 to 0x0000010000000000. Even though the kernel never
> generates memory accesses in that region, since the page tables mark
> them incorrectly as being WB, our (AMD) processor ends up causing a MCE
> while doing some memory bookkeeping/optimizations around that area.
>
> This patch iterates through e820 and only direct maps ranges that are
> marked as E820_RAM, and keeps track of those pfn ranges. Depending on
> the alignment of E820 ranges, this may possibly result in using smaller
> size (i.e. 4K instead of 2M or 1G) page tables.
>
> Signed-off-by: Jacob Shin <jacob.shin@....com>
> ---
> arch/x86/include/asm/page_types.h | 9 +++
> arch/x86/kernel/setup.c | 125 +++++++++++++++++++++++++++++--------
> arch/x86/mm/init.c | 2 +
> arch/x86/mm/init_64.c | 6 +-
> 4 files changed, 112 insertions(+), 30 deletions(-)
>
> diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
> index e21fdd1..409047a 100644
> --- a/arch/x86/include/asm/page_types.h
> +++ b/arch/x86/include/asm/page_types.h
> @@ -3,6 +3,7 @@
>
> #include <linux/const.h>
> #include <linux/types.h>
> +#include <asm/e820.h>
>
> /* PAGE_SHIFT determines the page size */
> #define PAGE_SHIFT 12
> @@ -40,12 +41,20 @@
> #endif /* CONFIG_X86_64 */
>
> #ifndef __ASSEMBLY__
> +#include <linux/range.h>
>
> extern int devmem_is_allowed(unsigned long pagenr);
>
> extern unsigned long max_low_pfn_mapped;
> extern unsigned long max_pfn_mapped;
>
> +extern struct range pfn_mapped[E820_X_MAX];
> +extern int nr_pfn_mapped;
> +
> +extern void add_pfn_range_mapped(unsigned long start_pfn, unsigned long end_pfn);
> +extern bool pfn_range_is_mapped(unsigned long start_pfn, unsigned long end_pfn);
> +extern bool pfn_is_mapped(unsigned long pfn);
> +
> static inline phys_addr_t get_max_mapped(void)
> {
> return (phys_addr_t)max_pfn_mapped << PAGE_SHIFT;
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index 751e020..4217fb4 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -115,13 +115,46 @@
> #include <asm/prom.h>
>
> /*
> - * end_pfn only includes RAM, while max_pfn_mapped includes all e820 entries.
> - * The direct mapping extends to max_pfn_mapped, so that we can directly access
> - * apertures, ACPI and other tables without having to play with fixmaps.
> + * max_low_pfn_mapped: highest direct mapped pfn under 4GB
> + * max_pfn_mapped: highest direct mapped pfn over 4GB
> + *
> + * The direct mapping only covers E820_RAM regions, so the ranges and gaps are
> + * represented by pfn_mapped
> */
> unsigned long max_low_pfn_mapped;
> unsigned long max_pfn_mapped;
>
> +struct range pfn_mapped[E820_X_MAX];
> +int nr_pfn_mapped;
> +
> +void add_pfn_range_mapped(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + nr_pfn_mapped = add_range_with_merge(pfn_mapped, E820_X_MAX,
> + nr_pfn_mapped, start_pfn, end_pfn);
> +
> + max_pfn_mapped = max(max_pfn_mapped, end_pfn);
> +
> + if (end_pfn <= (1UL << (32 - PAGE_SHIFT)))
> + max_low_pfn_mapped = max(max_low_pfn_mapped, end_pfn);
> +}
> +
> +bool pfn_range_is_mapped(unsigned long start_pfn, unsigned long end_pfn)
> +{
> + int i;
> +
> + for (i = 0; i < nr_pfn_mapped; i++)
> + if ((start_pfn >= pfn_mapped[i].start) &&
> + (end_pfn <= pfn_mapped[i].end))
> + return true;
> +
> + return false;
> +}
> +
> +bool pfn_is_mapped(unsigned long pfn)
> +{
> + return pfn_range_is_mapped(pfn, pfn + 1);
> +}
> +
looks like you could avoid add pfn_mapped[] array.
pfn_range_is_mapped() should be
check max_low_pfn_mapped, max_pfn_mapped with
e820_all_mapped(start, end, E820_RAM).
Thanks
Yinghai
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