[PATCH] KVM: Correct ordering of ldt reload wrt fs/gs reload

[PATCH] KVM: Correct ordering of ldt reload wrt fs/gs reload

[Avi Kivity]

If fs or gs refer to the ldt, they must be reloaded after the ldt.  Reorder
the code to that effect.

Userspace code that uses the ldt with kvm is nonexistent, so this doesn't fix
a user-visible bug.

Signed-off-by: Avi Kivity <avi@redhat.com>
---
 arch/x86/kvm/svm.c |    2 +-
 arch/x86/kvm/vmx.c |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f931a28..2e57450 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3418,6 +3418,7 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 	vcpu->arch.regs[VCPU_REGS_RIP] = svm->vmcb->save.rip;
 
 	load_host_msrs(vcpu);
+	kvm_load_ldt(ldt_selector);
 	loadsegment(fs, fs_selector);
 #ifdef CONFIG_X86_64
 	load_gs_index(gs_selector);
@@ -3425,7 +3426,6 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
 #else
 	loadsegment(gs, gs_selector);
 #endif
-	kvm_load_ldt(ldt_selector);
 
 	reload_tss(vcpu);
 
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 8da0e45..6fe7df75 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -839,8 +839,6 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
 
 	++vmx->vcpu.stat.host_state_reload;
 	vmx->host_state.loaded = 0;
-	if (vmx->host_state.fs_reload_needed)
-		loadsegment(fs, vmx->host_state.fs_sel);
 	if (vmx->host_state.gs_ldt_reload_needed) {
 		kvm_load_ldt(vmx->host_state.ldt_sel);
 #ifdef CONFIG_X86_64
@@ -850,6 +848,8 @@ static void __vmx_load_host_state(struct vcpu_vmx *vmx)
 		loadsegment(gs, vmx->host_state.gs_sel);
 #endif
 	}
+	if (vmx->host_state.fs_reload_needed)
+		loadsegment(fs, vmx->host_state.fs_sel);
 	reload_tss();
 #ifdef CONFIG_X86_64
 	if (is_long_mode(&vmx->vcpu)) {
-- 
1.7.3.1

Re: [PATCH] KVM: Correct ordering of ldt reload wrt fs/gs reload

[Marcelo Tosatti]

On Tue, Oct 19, 2010 at 06:48:35PM +0200, Avi Kivity wrote:
> If fs or gs refer to the ldt, they must be reloaded after the ldt.  Reorder
> the code to that effect.
> 
> Userspace code that uses the ldt with kvm is nonexistent, so this doesn't fix
> a user-visible bug.
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>

Applied, thanks.