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Re: [Xen-devel] [PATCH] x86/AMD: Add support for AMD's OSVW feature in guests

On 01/31/12 11:13, Jan Beulich wrote:
--- a/xen/arch/x86/platform_hypercall.c Thu Jan 26 17:43:31 2012 +0000
+++ b/xen/arch/x86/platform_hypercall.c Mon Jan 30 18:00:50 2012 +0100
@@ -166,7 +166,17 @@ ret_t do_platform_op(XEN_GUEST_HANDLE(xe

          guest_from_compat_handle(data, op->u.microcode.data);
+        while ( !domctl_lock_acquire() )

It's not clear to me what you're trying to protect against here. I don't
think this prevents guests from making progress (and hence possibly
seeing the intermediate [and wrong] OSVW state between
svm_host_osvw_reset() and svm_host_osvw_init()).

The reason is because when we allocated VCPUs (via XEN_DOMCTL_max_vcpus and possibly other controls) we call svm_vcpu_initialise() -> svm_guest_osvw_init(). If we are in the middle of microcode update then osvw_length/osvw_status may be in an inconsistent state.



+            if ( hypercall_preempt_check() )
+            {
+                ret = hypercall_create_continuation(
+                    __HYPERVISOR_platform_op, "h", u_xenpf_op);
+                goto out;
+            }
          ret = microcode_update(data, op->u.microcode.length);
+        domctl_lock_release();

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