From f5c24a7fd0798d636af184cc7032e7e0cb149112 Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Wed, 12 Mar 2008 03:53:30 +0100 Subject: [PATCH] x86: don't use large pages to map the first 2/4MB of memory Intel recommends to not use large pages for the first 1MB of the physical memory because there are fixed size MTRRs there which cause splitups in the TLBs. On AMD doing so is also a good idea. The implementation is a little different between 32bit and 64bit. On 32bit I just taught the initial page table set up about this because it was very simple to do. This also has the advantage that the risk of a prefetch ever seeing the page even if it only exists for a short time is minimized. On 64bit that is not quite possible, so use set_memory_4k() a little later (in check_bugs) instead. Signed-off-by: Andi Kleen Acked-by: andreas.herrmann3@amd.com Cc: mingo@elte.hu Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/kernel/bugs_64.c | 12 ++++++++++++ arch/x86/mm/init_32.c | 7 ++++++- 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/bugs_64.c b/arch/x86/kernel/bugs_64.c index 60207e999a..9a3ed0649d 100644 --- a/arch/x86/kernel/bugs_64.c +++ b/arch/x86/kernel/bugs_64.c @@ -9,6 +9,7 @@ #include #include #include +#include void __init check_bugs(void) { @@ -18,4 +19,15 @@ void __init check_bugs(void) print_cpu_info(&boot_cpu_data); #endif alternative_instructions(); + + /* + * Make sure the first 2MB area is not mapped by huge pages + * There are typically fixed size MTRRs in there and overlapping + * MTRRs into large pages causes slow downs. + * + * Right now we don't do that with gbpages because there seems + * very little benefit for that case. + */ + if (!direct_gbpages) + set_memory_4k((unsigned long)__va(0), 1); } diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c index fc3ace2e88..1500dc8d63 100644 --- a/arch/x86/mm/init_32.c +++ b/arch/x86/mm/init_32.c @@ -181,8 +181,13 @@ static void __init kernel_physical_mapping_init(pgd_t *pgd_base) /* * Map with big pages if possible, otherwise * create normal page tables: + * + * Don't use a large page for the first 2/4MB of memory + * because there are often fixed size MTRRs in there + * and overlapping MTRRs into large pages can cause + * slowdowns. */ - if (cpu_has_pse) { + if (cpu_has_pse && !(pgd_idx == 0 && pmd_idx == 0)) { unsigned int addr2; pgprot_t prot = PAGE_KERNEL_LARGE; -- 2.39.5