[PATCH v1 2/6] nestedsvm: Adjust L2's DR intercept when adjusting L1

[Ross Lagerwall <ross.lagerwall@citrix.com>]

If L2 accesses a debug register (like reading DR7) without L1 intercepting
it, it locks up the vCPU. L0 intercepts VMEXIT_DR7_READ, which disables
the intercept for L1 and then restarts L2 which re-executes the
instruction and then this repeats indefinitely.

Disable the intercept for the current VMCB if in guest mode to reflect
what would happen if the VMCB were recreated via
nsvm_vmcb_prepare4vmrun().

Fixes: a59a7be91b61 ("nestedsvm: fix DRn handling")
Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
---
 xen/arch/x86/hvm/svm/svm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 49fcdd906cf8..209edcba321a 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -1657,6 +1657,8 @@ static void svm_dr_access(struct vcpu *v, struct cpu_user_regs *regs)
 
     TRACE(TRC_HVM_DR_WRITE);
     __restore_debug_registers(vmcb, v);
+    if ( nestedhvm_enabled(v->domain) && nestedhvm_vcpu_in_guestmode(v) )
+        vmcb_set_dr_intercepts(v->arch.hvm.svm.vmcb, 0);
 }
 
 static int cf_check svm_msr_read_intercept(
-- 
2.53.0