Hello, In extras/mini-os/arch/x86/mm.c:new_pt_frame, Mini-OS pins its L1, L2, and L3 page tables. Does that really make a difference from the Hypervisor point of view? I mean, once L4 is pinned, pointing to these, and thus their content has been checked, is there any performance difference? Samuel _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
No, there''s not really any need to pin anything other than the top-level directory. -- Keir On 27/5/08 11:17, "Samuel Thibault" <samuel.thibault@eu.citrix.com> wrote:> Hello, > > In extras/mini-os/arch/x86/mm.c:new_pt_frame, Mini-OS pins its L1, > L2, and L3 page tables. Does that really make a difference from the > Hypervisor point of view? I mean, once L4 is pinned, pointing to these, > and thus their content has been checked, is there any performance > difference? > > Samuel > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Samuel Thibault wrote:> Hello, > > In extras/mini-os/arch/x86/mm.c:new_pt_frame, Mini-OS pins its L1, > L2, and L3 page tables. Does that really make a difference from the > Hypervisor point of view? I mean, once L4 is pinned, pointing to these, > and thus their content has been checked, is there any performance > difference? >Shouldn''t be. Pinning an L4 implicitly pins everything else below it. The only reason to pin the leafy parts of a pagetable is if you want to play games with incrementally pinning the pagetable, or if you want to pull them apart and rearrange the pieces for some reason. For example, I do incremental pagetable pins in the Xen/pvops kernel to limit the number of pte locks I need to hold at any one time. J _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Samuel Thibault
2008-May-27 10:58 UTC
Re: [Xen-devel] [PATCH] minios: do not pin page tables [was: Really need to pin page tables?]
Jeremy Fitzhardinge, le Tue 27 May 2008 11:49:33 +0100, a écrit :> Samuel Thibault wrote: > >Hello, > > > >In extras/mini-os/arch/x86/mm.c:new_pt_frame, Mini-OS pins its L1, > >L2, and L3 page tables. Does that really make a difference from the > >Hypervisor point of view? I mean, once L4 is pinned, pointing to these, > >and thus their content has been checked, is there any performance > >difference? > > > > Shouldn''t be. Pinning an L4 implicitly pins everything else below it. > The only reason to pin the leafy parts of a pagetable is if you want to > play games with incrementally pinning the pagetable, or if you want to > pull them apart and rearrange the pieces for some reason. For example, > I do incremental pagetable pins in the Xen/pvops kernel to limit the > number of pte locks I need to hold at any one time.Ok, that''s what I had in mind indeed. Here is a patch to drop that from Mini-OS. Samuel minios: We do not need to pin the page tables, as they implicitely get pinned when we point the permanent page directory to them. Signed-off-by: Samuel Thibault <samuel.thibault@eu.citrix.com> diff -r 2141ac752316 extras/mini-os/arch/x86/mm.c --- a/extras/mini-os/arch/x86/mm.c Fri May 23 15:43:32 2008 +0100 +++ b/extras/mini-os/arch/x86/mm.c Tue May 27 11:51:43 2008 +0100 @@ -59,11 +59,10 @@ { pgentry_t *tab = (pgentry_t *)start_info.pt_base; unsigned long pt_page = (unsigned long)pfn_to_virt(*pt_pfn); - unsigned long prot_e, prot_t, pincmd; + unsigned long prot_e, prot_t; mmu_update_t mmu_updates[1]; - struct mmuext_op pin_request; - prot_e = prot_t = pincmd = 0; + prot_e = prot_t = 0; DEBUG("Allocating new L%d pt frame for pt_pfn=%lx, " "prev_l_mfn=%lx, offset=%lx", level, *pt_pfn, prev_l_mfn, offset); @@ -77,18 +76,15 @@ case L1_FRAME: prot_e = L1_PROT; prot_t = L2_PROT; - pincmd = MMUEXT_PIN_L1_TABLE; break; case L2_FRAME: prot_e = L2_PROT; prot_t = L3_PROT; - pincmd = MMUEXT_PIN_L2_TABLE; break; #if defined(__x86_64__) case L3_FRAME: prot_e = L3_PROT; prot_t = L4_PROT; - pincmd = MMUEXT_PIN_L3_TABLE; break; #endif default: @@ -113,15 +109,6 @@ do_exit(); } - /* Pin the page to provide correct protection */ - pin_request.cmd = pincmd; - pin_request.arg1.mfn = pfn_to_mfn(*pt_pfn); - if(HYPERVISOR_mmuext_op(&pin_request, 1, NULL, DOMID_SELF) < 0) - { - printk("ERROR: pinning failed\n"); - do_exit(); - } - /* Now fill the new page table page with entries. Update the page directory as well. */ mmu_updates[0].ptr = ((pgentry_t)prev_l_mfn << PAGE_SHIFT) + sizeof(pgentry_t) * offset; _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel