Commit 0cc9129d authored by Committed by Linus Torvalds
x86-64, xen, mmu: Provide an early version of write_cr3.
With commit 8170e6be ("x86, 64bit: Use a #PF handler to materialize early mappings on demand") we started hitting an early bootup crash where the Xen hypervisor would inform us that: (XEN) d7:v0: unhandled page fault (ec=0000) (XEN) Pagetable walk from ffffea000005b2d0: (XEN) L4[0x1d4] = 0000000000000000 ffffffffffffffff (XEN) domain_crash_sync called from entry.S (XEN) Domain 7 (vcpu#0) crashed on cpu#3: (XEN) ----[ Xen-4.2.0 x86_64 debug=n Not tainted ]---- .. that Xen was unable to context switch back to dom0. Looking at the calling stack we find: [<ffffffff8103feba>] xen_get_user_pgd+0x5a <-- [<ffffffff8103feba>] xen_get_user_pgd+0x5a [<ffffffff81042d27>] xen_write_cr3+0x77 [<ffffffff81ad2d21>] init_mem_mapping+0x1f9 [<ffffffff81ac293f>] setup_arch+0x742 [<ffffffff81666d71>] printk+0x48 We are trying to figure out whether we need to up-date the user PGD as well. Please keep in mind that under 64-bit PV guests we have a limited amount of rings: 0 for the Hypervisor, and 1 for both the Linux kernel and user-space. As such the Linux pvops'fied version of write_cr3 checks if it has to update the user-space cr3 as well. That clearly is not needed during early bootup. The recent changes (see above git commit) streamline the x86 page table allocation to be much simpler (And also incidentally the #PF handler ends up in spirit being similar to how the Xen toolstack sets up the initial page-tables). The fix is to have an early-bootup version of cr3 that just loads the kernel %cr3. The later version - which also handles user-page modifications will be used after the initial page tables have been setup. [ hpa: removed a redundant #ifdef and made the new function __init. Also note that x86-32 already has such an early xen_write_cr3. ] Tested-by: "H. Peter Anvin" <email@example.com> Reported-by: Konrad Rzeszutek Wilk <firstname.lastname@example.org> Signed-off-by: Konrad Rzeszutek Wilk <email@example.com> Link: http://firstname.lastname@example.orgSigned-off-by: H. Peter Anvin <email@example.com> Signed-off-by: Linus Torvalds <firstname.lastname@example.org>
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