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authorStefano Stabellini <stefano.stabellini@eu.citrix.com>2011-04-14 15:49:41 +0100
committerKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>2011-05-12 13:05:04 -0400
commit279b706bf800b5967037f492dbe4fc5081ad5d0f (patch)
tree608b9455cd6af84018bd5096b45e0ca90f9c7619 /arch/x86/kernel/x86_init.c
parent92bdaef7b2c5d3cb8abc902faa1f7670a183dcdc (diff)
x86,xen: introduce x86_init.mapping.pagetable_reserve
Introduce a new x86_init hook called pagetable_reserve that at the end of init_memory_mapping is used to reserve a range of memory addresses for the kernel pagetable pages we used and free the other ones. On native it just calls memblock_x86_reserve_range while on xen it also takes care of setting the spare memory previously allocated for kernel pagetable pages from RO to RW, so that it can be used for other purposes. A detailed explanation of the reason why this hook is needed follows. As a consequence of the commit: commit 4b239f458c229de044d6905c2b0f9fe16ed9e01e Author: Yinghai Lu <yinghai@kernel.org> Date: Fri Dec 17 16:58:28 2010 -0800 x86-64, mm: Put early page table high at some point init_memory_mapping is going to reach the pagetable pages area and map those pages too (mapping them as normal memory that falls in the range of addresses passed to init_memory_mapping as argument). Some of those pages are already pagetable pages (they are in the range pgt_buf_start-pgt_buf_end) therefore they are going to be mapped RO and everything is fine. Some of these pages are not pagetable pages yet (they fall in the range pgt_buf_end-pgt_buf_top; for example the page at pgt_buf_end) so they are going to be mapped RW. When these pages become pagetable pages and are hooked into the pagetable, xen will find that the guest has already a RW mapping of them somewhere and fail the operation. The reason Xen requires pagetables to be RO is that the hypervisor needs to verify that the pagetables are valid before using them. The validation operations are called "pinning" (more details in arch/x86/xen/mmu.c). In order to fix the issue we mark all the pages in the entire range pgt_buf_start-pgt_buf_top as RO, however when the pagetable allocation is completed only the range pgt_buf_start-pgt_buf_end is reserved by init_memory_mapping. Hence the kernel is going to crash as soon as one of the pages in the range pgt_buf_end-pgt_buf_top is reused (b/c those ranges are RO). For this reason we need a hook to reserve the kernel pagetable pages we used and free the other ones so that they can be reused for other purposes. On native it just means calling memblock_x86_reserve_range, on Xen it also means marking RW the pagetable pages that we allocated before but that haven't been used before. Another way to fix this is without using the hook is by adding a 'if (xen_pv_domain)' in the 'init_memory_mapping' code and calling the Xen counterpart, but that is just nasty. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> Acked-by: Yinghai Lu <yinghai@kernel.org> Acked-by: H. Peter Anvin <hpa@zytor.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Diffstat (limited to 'arch/x86/kernel/x86_init.c')
-rw-r--r--arch/x86/kernel/x86_init.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index c11514e9128b..75ef4b18e9b7 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -61,6 +61,10 @@ struct x86_init_ops x86_init __initdata = {
.banner = default_banner,
},
+ .mapping = {
+ .pagetable_reserve = native_pagetable_reserve,
+ },
+
.paging = {
.pagetable_setup_start = native_pagetable_setup_start,
.pagetable_setup_done = native_pagetable_setup_done,