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@xxxxxxxxxxxxx>
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;
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