x86/svm: Use flush-by-asid when available

AMD Fam15h processors introduced the flush-by-asid feature, for more fine
grain flushing purposes.

Flushing everything including ASID 0 (i.e. Xen context) is an an unnecesserily
large hammer, and never necessary in the context of guest TLBs needing
invalidating.

When available, use TLB_CTRL_FLUSH_ASID in preference to TLB_CTRL_FLUSH_ALL.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/hvm/svm/asid.c

@@ -18,6 +18,7 @@
 #include <asm/amd.h>
 #include <asm/hvm/nestedhvm.h>
 #include <asm/hvm/svm/asid.h>
+#include <asm/hvm/svm/svm.h>
 
 void svm_asid_init(const struct cpuinfo_x86 *c)
 {
@@ -47,15 +48,17 @@ void svm_asid_handle_vmrun(void)
     if ( p_asid->asid == 0 )
     {
         vmcb_set_guest_asid(vmcb, 1);
-        /* TODO: investigate using TLB_CTRL_FLUSH_ASID here instead. */
-        vmcb->tlb_control = TLB_CTRL_FLUSH_ALL;
+        vmcb->tlb_control =
+            cpu_has_svm_flushbyasid ? TLB_CTRL_FLUSH_ASID : TLB_CTRL_FLUSH_ALL;
         return;
     }
 
     if ( vmcb_get_guest_asid(vmcb) != p_asid->asid )
         vmcb_set_guest_asid(vmcb, p_asid->asid);
 
-    vmcb->tlb_control = need_flush ? TLB_CTRL_FLUSH_ALL : TLB_CTRL_NO_FLUSH;
+    vmcb->tlb_control =
+        !need_flush ? TLB_CTRL_NO_FLUSH :
+        cpu_has_svm_flushbyasid ? TLB_CTRL_FLUSH_ASID : TLB_CTRL_FLUSH_ALL;
 }
 
 /*

xen/include/asm-x86/hvm/svm/svm.h

@@ -79,6 +79,7 @@ extern u32 svm_feature_flags;
 #define cpu_has_svm_svml      cpu_has_svm_feature(SVM_FEATURE_SVML)
 #define cpu_has_svm_nrips     cpu_has_svm_feature(SVM_FEATURE_NRIPS)
 #define cpu_has_svm_cleanbits cpu_has_svm_feature(SVM_FEATURE_VMCBCLEAN)
+#define cpu_has_svm_flushbyasid cpu_has_svm_feature(SVM_FEATURE_FLUSHBYASID)
 #define cpu_has_svm_decode    cpu_has_svm_feature(SVM_FEATURE_DECODEASSISTS)
 #define cpu_has_svm_vgif      cpu_has_svm_feature(SVM_FEATURE_VGIF)
 #define cpu_has_pause_filter  cpu_has_svm_feature(SVM_FEATURE_PAUSEFILTER)