| From | Kamal Mostafa <> | Subject | [PATCH 3.13.y-ckt 009/156] KVM: emulate: fix CMPXCHG8B on 32-bit hosts | Date | Tue, 7 Apr 2015 15:49:06 -0700 |
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3.13.11-ckt19 -stable review patch. If anyone has any objections, please let me know.
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From: Paolo Bonzini <pbonzini@redhat.com>
commit 4ff6f8e61eb7f96d3ca535c6d240f863ccd6fb7d upstream.
This has been broken for a long time: it broke first in 2.6.35, then was almost fixed in 2.6.36 but this one-liner slipped through the cracks. The bug shows up as an infinite loop in Windows 7 (and newer) boot on 32-bit hosts without EPT.
Windows uses CMPXCHG8B to write to page tables, which causes a page fault if running without EPT; the emulator is then called from kvm_mmu_page_fault. The loop then happens if the higher 4 bytes are not 0; the common case for this is that the NX bit (bit 63) is 1.
Fixes: 6550e1f165f384f3a46b60a1be9aba4bc3c2adad Fixes: 16518d5ada690643453eb0aef3cc7841d3623c2d Reported-by: Erik Rull <erik.rull@rdsoftware.de> Tested-by: Erik Rull <erik.rull@rdsoftware.de> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- arch/x86/kvm/emulate.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 9c35870..477e61e 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4708,7 +4708,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) if (rc != X86EMUL_CONTINUE) goto done; } - ctxt->dst.orig_val = ctxt->dst.val; + /* Copy full 64-bit value for CMPXCHG8B. */ + ctxt->dst.orig_val64 = ctxt->dst.val64; special_insn: -- 1.9.1
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