Commit 4ff6f8e6 authored by Paolo Bonzini's avatar Paolo Bonzini

KVM: emulate: fix CMPXCHG8B on 32-bit hosts

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: 6550e1f1
Fixes: 16518d5a
Cc: stable@vger.kernel.org   # 2.6.35+
Reported-by: default avatarErik Rull <erik.rull@rdsoftware.de>
Tested-by: default avatarErik Rull <erik.rull@rdsoftware.de>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 21bc8dc5
...@@ -4950,7 +4950,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) ...@@ -4950,7 +4950,8 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
goto done; 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: special_insn:
......
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