>> The complications in my patch come >> from the fact that the vsyscall page has to be relocated dynamically, >> requiring, basically run time linking on the page and some tweaks to get >> sysenter to work. If you don't use vsyscall (say, non-TLS glibc), then >> you don't need that complexity. But I think it might be needed now, >> even for Xen. > > I believe both Xen and execshield move vsyscall out of fixmap, and then > map into userspace as normal vma. Yep, my patch (attached below for reference) moves the vsyscall page into user address space, just below PAGE_OFFSET. Works basically the same way the vsyscall page is mapped in the ia32 emulation of the x86_64 architecture. Address stays fixed, thus the relocation magic isn't needed. Once the vsyscall page is moved out of fixmap it's easy to make fixmap movable and thus have a runtime-resizable address space hole at the top of address space. Patch is attached too, although that one is more proof-of-concept, it doesn't make much sense as-is. It has a kernel command line option to specify the top of address space so you can play around with it ... Both patches are against -rc3 and most likely still apply just fine, havn't tested that though. cheers, Gerd -- Gerd 'just married' Hoffmann <kraxel@xxxxxxx> I'm the hacker formerly known as Gerd Knorr. http://www.suse.de/~kraxel/just-married.jpeg -------------- next part -------------- A non-text attachment was scrubbed... Name: move-gate-page.diff Type: text/x-patch Size: 6955 bytes Desc: not available Url : http://lists.osdl.org/pipermail/virtualization/attachments/20060315/7b7142b9/move-gate-page-0001.bin -------------- next part -------------- Index: vanilla-2.6.16-rc3/arch/i386/kernel/setup.c =================================================================== --- vanilla-2.6.16-rc3.orig/arch/i386/kernel/setup.c 2006-02-13 09:39:33.000000000 +0100 +++ vanilla-2.6.16-rc3/arch/i386/kernel/setup.c 2006-02-13 09:57:36.000000000 +0100 @@ -922,6 +922,12 @@ static void __init parse_cmdline_early ( else if (!memcmp(from, "vmalloc=", 8)) __VMALLOC_RESERVE = memparse(from+8, &from); + /* + * fixmap=addr + */ + else if (!memcmp(from, "fixmap=", 7)) + set_fixaddr_top(simple_strtoul(from+7, NULL, 16)); + next_char: c = *(from++); if (!c) Index: vanilla-2.6.16-rc3/arch/i386/mm/init.c =================================================================== --- vanilla-2.6.16-rc3.orig/arch/i386/mm/init.c 2006-02-13 09:39:33.000000000 +0100 +++ vanilla-2.6.16-rc3/arch/i386/mm/init.c 2006-02-13 14:33:40.000000000 +0100 @@ -628,6 +628,42 @@ void __init mem_init(void) (unsigned long) (totalhigh_pages << (PAGE_SHIFT-10)) ); +#if 1 /* double-sanity-check paranoia */ + printk("virtual kernel memory layout:\n" + " fixmap : 0x%08lx - 0x%08lx (%4ld kB)\n" + " pkmap : 0x%08lx - 0x%08lx (%4ld kB)\n" + " vmalloc : 0x%08lx - 0x%08lx (%4ld MB)\n" + " lowmem : 0x%08lx - 0x%08lx (%4ld MB)\n" + " .init : 0x%08lx - 0x%08lx (%4ld kB)\n" + " .data : 0x%08lx - 0x%08lx (%4ld kB)\n" + " .text : 0x%08lx - 0x%08lx (%4ld kB)\n", + FIXADDR_START, FIXADDR_TOP, + (FIXADDR_TOP - FIXADDR_START) >> 10, + + PKMAP_BASE, PKMAP_BASE+LAST_PKMAP*PAGE_SIZE, + (LAST_PKMAP*PAGE_SIZE) >> 10, + + VMALLOC_START, VMALLOC_END, + (VMALLOC_END - VMALLOC_START) >> 20, + + (unsigned long)__va(0), (unsigned long)high_memory, + ((unsigned long)high_memory - (unsigned long)__va(0)) >> 20, + + (unsigned long)&__init_begin, (unsigned long)&__init_end, + ((unsigned long)&__init_end - (unsigned long)&__init_begin) >> 10, + + (unsigned long)&_etext, (unsigned long)&_edata, + ((unsigned long)&_edata - (unsigned long)&_etext) >> 10, + + (unsigned long)&_text, (unsigned long)&_etext, + ((unsigned long)&_etext - (unsigned long)&_text) >> 10); + + BUG_ON(PKMAP_BASE+LAST_PKMAP*PAGE_SIZE > FIXADDR_START); + BUG_ON(VMALLOC_END > PKMAP_BASE); + BUG_ON(VMALLOC_START > VMALLOC_END); + BUG_ON((unsigned long)high_memory > VMALLOC_START); +#endif /* double-sanity-check paranoia */ + #ifdef CONFIG_X86_PAE if (!cpu_has_pae) panic("cannot execute a PAE-enabled kernel on a PAE-less CPU!"); Index: vanilla-2.6.16-rc3/arch/i386/mm/pgtable.c =================================================================== --- vanilla-2.6.16-rc3.orig/arch/i386/mm/pgtable.c 2006-01-03 04:21:10.000000000 +0100 +++ vanilla-2.6.16-rc3/arch/i386/mm/pgtable.c 2006-02-13 09:57:36.000000000 +0100 @@ -13,6 +13,7 @@ #include <linux/slab.h> #include <linux/pagemap.h> #include <linux/spinlock.h> +#include <linux/module.h> #include <asm/system.h> #include <asm/pgtable.h> @@ -138,6 +139,10 @@ void set_pmd_pfn(unsigned long vaddr, un __flush_tlb_one(vaddr); } +static int fixmaps = 0; +unsigned long __FIXADDR_TOP = 0xfffff000; +EXPORT_SYMBOL(__FIXADDR_TOP); + void __set_fixmap (enum fixed_addresses idx, unsigned long phys, pgprot_t flags) { unsigned long address = __fix_to_virt(idx); @@ -147,6 +152,14 @@ void __set_fixmap (enum fixed_addresses return; } set_pte_pfn(address, phys >> PAGE_SHIFT, flags); + fixmaps++; +} + +void set_fixaddr_top(unsigned long top) +{ + BUG_ON(fixmaps > 0); + printk("%s: addr=0x%lx\n", __FUNCTION__, top); + __FIXADDR_TOP = top - PAGE_SIZE; } pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address) Index: vanilla-2.6.16-rc3/include/asm-i386/fixmap.h =================================================================== --- vanilla-2.6.16-rc3.orig/include/asm-i386/fixmap.h 2006-02-13 09:57:36.000000000 +0100 +++ vanilla-2.6.16-rc3/include/asm-i386/fixmap.h 2006-02-13 09:57:36.000000000 +0100 @@ -20,7 +20,7 @@ * Leave one empty page between vmalloc'ed areas and * the start of the fixmap. */ -#define __FIXADDR_TOP 0xfffff000 +extern unsigned long __FIXADDR_TOP; #ifndef __ASSEMBLY__ #include <linux/kernel.h> @@ -93,6 +93,7 @@ enum fixed_addresses { extern void __set_fixmap (enum fixed_addresses idx, unsigned long phys, pgprot_t flags); +extern void set_fixaddr_top(unsigned long top); #define set_fixmap(idx, phys) \ __set_fixmap(idx, phys, PAGE_KERNEL) Index: vanilla-2.6.16-rc3/include/asm-i386/page.h =================================================================== --- vanilla-2.6.16-rc3.orig/include/asm-i386/page.h 2006-02-13 09:57:36.000000000 +0100 +++ vanilla-2.6.16-rc3/include/asm-i386/page.h 2006-02-13 14:21:36.000000000 +0100 @@ -121,7 +121,7 @@ extern int page_is_ram(unsigned long pag #define PAGE_OFFSET ((unsigned long)__PAGE_OFFSET) #define VMALLOC_RESERVE ((unsigned long)__VMALLOC_RESERVE) -#define MAXMEM (-__PAGE_OFFSET-__VMALLOC_RESERVE) +#define MAXMEM (__FIXADDR_TOP-__PAGE_OFFSET-__VMALLOC_RESERVE) #define __pa(x) ((unsigned long)(x)-PAGE_OFFSET) #define __va(x) ((void *)((unsigned long)(x)+PAGE_OFFSET)) #define pfn_to_kaddr(pfn) __va((pfn) << PAGE_SHIFT)