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KVM: SVM: Make sure KERNEL_GS_BASE is valid when loading gs_index 

The gs_index loading code uses the swapgs instruction to
switch to the user gs_base temporarily. This is unsave in an
lightweight exit-path in KVM on AMD because the
KERNEL_GS_BASE MSR is switches lazily. An NMI happening in
the critical path of load_gs_index may use the wrong GS_BASE
value then leading to unpredictable behavior, e.g. a
triple-fault.

This patch fixes the issue by making sure that load_gs_index
is called only with a valid KERNEL_GS_BASE value loaded in
KVM.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Joerg Roedel 2011-01-14 16:45:01 +01:00 committed by Avi Kivity
parent 0b0abeaf3d
commit 893a5ab6ee
1 changed files with 1 additions and 1 deletions
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2
arch/x86/kvm/svm.c
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@ -1150,8 +1150,8 @@ static void svm_vcpu_put(struct kvm_vcpu *vcpu)
kvm_load_ldt(svm->host.ldt);
#ifdef CONFIG_X86_64
loadsegment(fs, svm->host.fs);
load_gs_index(svm->host.gs);
wrmsrl(MSR_KERNEL_GS_BASE, current->thread.gs);
load_gs_index(svm->host.gs);
#else
loadsegment(gs, svm->host.gs);
#endif