Messages in this thread Patch in this message | | | From | Jiri Slaby <> | Subject | [PATCH 3.12 109/175] KVM: emulate: fix CMPXCHG8B on 32-bit hosts | Date | Tue, 17 Mar 2015 09:41:27 +0100 |
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From: Paolo Bonzini <pbonzini@redhat.com>
3.12-stable review patch. If anyone has any objections, please let me know.
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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: Jiri Slaby <jslaby@suse.cz> --- 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 8ab43ac68f06..c412bab82d1f 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -4617,7 +4617,8 @@ 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: -- 2.3.0
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