106 lines
3.3 KiB
Diff
106 lines
3.3 KiB
Diff
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References: bnc#846849
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# Commit 58929248461ecadce13e92eb5a5d9ef718a7c88e
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# Date 2013-11-12 11:52:19 +0100
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# Author Jan Beulich <jbeulich@suse.com>
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# Committer Jan Beulich <jbeulich@suse.com>
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VMX: don't crash processing 'd' debug key
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There's a window during scheduling where "current" and the active VMCS
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may disagree: The former gets set much earlier than the latter. Since
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both vmx_vmcs_enter() and vmx_vmcs_exit() immediately return when the
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subject vCPU is "current", accessing VMCS fields would, depending on
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whether there is any currently active VMCS, either read wrong data, or
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cause a crash.
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Going forward we might want to consider reducing the window during
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which vmx_vmcs_enter() might fail (e.g. doing a plain __vmptrld() when
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v->arch.hvm_vmx.vmcs != this_cpu(current_vmcs) but arch_vmx->active_cpu
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== -1), but that would add complexities (acquiring and - more
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importantly - properly dropping v->arch.hvm_vmx.vmcs_lock) that don't
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look worthwhile adding right now.
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Signed-off-by: Jan Beulich <jbeulich@suse.com>
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Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
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Acked-by: Keir Fraser <keir@xen.org>
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--- a/xen/arch/x86/hvm/vmx/vmcs.c
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+++ b/xen/arch/x86/hvm/vmx/vmcs.c
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@@ -591,16 +591,16 @@ struct foreign_vmcs {
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};
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static DEFINE_PER_CPU(struct foreign_vmcs, foreign_vmcs);
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-void vmx_vmcs_enter(struct vcpu *v)
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+bool_t vmx_vmcs_try_enter(struct vcpu *v)
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{
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struct foreign_vmcs *fv;
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/*
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* NB. We must *always* run an HVM VCPU on its own VMCS, except for
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- * vmx_vmcs_enter/exit critical regions.
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+ * vmx_vmcs_enter/exit and scheduling tail critical regions.
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*/
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if ( likely(v == current) )
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- return;
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+ return v->arch.hvm_vmx.vmcs == this_cpu(current_vmcs);
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fv = &this_cpu(foreign_vmcs);
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@@ -623,6 +623,15 @@ void vmx_vmcs_enter(struct vcpu *v)
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}
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fv->count++;
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+
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+ return 1;
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+}
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+
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+void vmx_vmcs_enter(struct vcpu *v)
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+{
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+ bool_t okay = vmx_vmcs_try_enter(v);
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+
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+ ASSERT(okay);
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}
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void vmx_vmcs_exit(struct vcpu *v)
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--- a/xen/arch/x86/hvm/vmx/vmx.c
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+++ b/xen/arch/x86/hvm/vmx/vmx.c
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@@ -669,7 +669,27 @@ void vmx_get_segment_register(struct vcp
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{
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uint32_t attr = 0;
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- vmx_vmcs_enter(v);
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+ /*
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+ * We may get here in the context of dump_execstate(), which may have
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+ * interrupted context switching between setting "current" and
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+ * vmx_do_resume() reaching the end of vmx_load_vmcs(). That would make
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+ * all the VMREADs below fail if we don't bail right away.
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+ */
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+ if ( unlikely(!vmx_vmcs_try_enter(v)) )
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+ {
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+ static bool_t warned;
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+
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+ if ( !warned )
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+ {
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+ warned = 1;
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+ printk(XENLOG_WARNING "Segment register inaccessible for d%dv%d\n"
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+ "(If you see this outside of debugging activity,"
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+ " please report to xen-devel@lists.xenproject.org)\n",
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+ v->domain->domain_id, v->vcpu_id);
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+ }
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+ memset(reg, 0, sizeof(*reg));
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+ return;
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+ }
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switch ( seg )
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{
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--- a/xen/include/asm-x86/hvm/vmx/vmcs.h
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+++ b/xen/include/asm-x86/hvm/vmx/vmcs.h
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@@ -144,6 +144,7 @@ struct arch_vmx_struct {
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int vmx_create_vmcs(struct vcpu *v);
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void vmx_destroy_vmcs(struct vcpu *v);
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void vmx_vmcs_enter(struct vcpu *v);
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+bool_t __must_check vmx_vmcs_try_enter(struct vcpu *v);
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void vmx_vmcs_exit(struct vcpu *v);
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#define CPU_BASED_VIRTUAL_INTR_PENDING 0x00000004
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