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Commit f48b4711 authored by Liran Alon's avatar Liran Alon Committed by Paolo Bonzini
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KVM: VMX: Update shared MSRs to be saved/restored on MSR_EFER.LMA changes 



When guest transitions from/to long-mode by modifying MSR_EFER.LMA,
the list of shared MSRs to be saved/restored on guest<->host
transitions is updated (See vmx_set_efer() call to setup_msrs()).

On every entry to guest, vcpu_enter_guest() calls
vmx_prepare_switch_to_guest(). This function should also take care
of setting the shared MSRs to be saved/restored. However, the
function does nothing in case we are already running with loaded
guest state (vmx->loaded_cpu_state != NULL).

This means that even when guest modifies MSR_EFER.LMA which results
in updating the list of shared MSRs, it isn't being taken into account
by vmx_prepare_switch_to_guest() because it happens while we are
running with loaded guest state.

To fix above mentioned issue, add a flag to mark that the list of
shared MSRs has been updated and modify vmx_prepare_switch_to_guest()
to set shared MSRs when running with host state *OR* list of shared
MSRs has been updated.

Note that this issue was mistakenly introduced by commit
678e315e ("KVM: vmx: add dedicated utility to access guest's
kernel_gs_base") because previously vmx_set_efer() always called
vmx_load_host_state() which resulted in vmx_prepare_switch_to_guest() to
set shared MSRs.

Fixes: 678e315e ("KVM: vmx: add dedicated utility to access guest's kernel_gs_base")
Reported-by: default avatarEyal Moscovici <eyal.moscovici@oracle.com>
Reviewed-by: default avatarMihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: default avatarLiam Merwick <liam.merwick@oracle.com>
Reviewed-by: default avatarJim Mattson <jmattson@google.com>
Signed-off-by: default avatarLiran Alon <liran.alon@oracle.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent bcbfbd8e

arch/x86/kvm/vmx.c

+16 −5
Original line number Diff line number Diff line
@@ -985,6 +985,7 @@ struct vcpu_vmx { 
	struct shared_msr_entry *guest_msrs;

	int                   nmsrs;

	int                   save_nmsrs;

	bool                  guest_msrs_dirty;

	unsigned long	      host_idt_base;

#ifdef CONFIG_X86_64

	u64 		      msr_host_kernel_gs_base;
@@ -2898,6 +2899,20 @@ static void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) 


	vmx->req_immediate_exit = false;



	/*

	 * Note that guest MSRs to be saved/restored can also be changed

	 * when guest state is loaded. This happens when guest transitions

	 * to/from long-mode by setting MSR_EFER.LMA.

	 */

	if (!vmx->loaded_cpu_state || vmx->guest_msrs_dirty) {

		vmx->guest_msrs_dirty = false;

		for (i = 0; i < vmx->save_nmsrs; ++i)

			kvm_set_shared_msr(vmx->guest_msrs[i].index,

					   vmx->guest_msrs[i].data,

					   vmx->guest_msrs[i].mask);



	}



	if (vmx->loaded_cpu_state)

		return;
@@ -2958,11 +2973,6 @@ static void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) 
		vmcs_writel(HOST_GS_BASE, gs_base);

		host_state->gs_base = gs_base;

	}



	for (i = 0; i < vmx->save_nmsrs; ++i)

		kvm_set_shared_msr(vmx->guest_msrs[i].index,

				   vmx->guest_msrs[i].data,

				   vmx->guest_msrs[i].mask);

}



static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
@@ -3437,6 +3447,7 @@ static void setup_msrs(struct vcpu_vmx *vmx) 
		move_msr_up(vmx, index, save_nmsrs++);



	vmx->save_nmsrs = save_nmsrs;

	vmx->guest_msrs_dirty = true;



	if (cpu_has_vmx_msr_bitmap())

		vmx_update_msr_bitmap(&vmx->vcpu);