[Xen-devel] [PATCH] VMX: wbinvd when vmentry under UC

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

From e2d47e2f75bac6876b7c2eaecfe946966bf27516 Mon Sep 17 00:00:00 2001
From: Liu Jinsong <jinsong.liu@xxxxxxxxx>
Date: Tue, 26 Nov 2013 04:53:17 +0800
Subject: [PATCH] VMX: wbinvd when vmentry under UC

This patch flush cache when vmentry back to UC guest, to prevent
cache polluted by hypervisor access guest memory during UC mode.

However, wbinvd is a _very_ time consuming operation, so
1. wbinvd ... timer has a good possibility to expire while
   irq disabled, it then would be delayed until
2. ... vmentry back to guest (and irq enalbed), timer interrupt
   then occurs and drops guest at once;
3. drop to hypervisor ... then vmentry and wbinvd again;

This loop will run again and again, until lucky enough wbinvd
happens not to expire timer and then loop break, usually it would
occur 10K~60K times, blocking guest 10s~60s.

reprogram timer to avoid dead_like_loop.

Signed-off-by: Liu Jinsong <jinsong.liu@xxxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c |   32 ++++++++++++++++++++++++++++----
 1 files changed, 28 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 75be62e..4768c9b 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -642,10 +642,6 @@ static void vmx_ctxt_switch_to(struct vcpu *v)
             __invept(INVEPT_SINGLE_CONTEXT, ept_get_eptp(ept_data), 0);
     }
 
-    /* For guest cr0.cd setting, do not use potentially polluted cache */
-    if ( unlikely(v->arch.hvm_vcpu.cache_mode == NO_FILL_CACHE_MODE) )
-        wbinvd();
-
     vmx_restore_guest_msrs(v);
     vmx_restore_dr(v);
 }
@@ -2967,6 +2963,27 @@ out:
         nvmx_idtv_handling();
 }
 
+/*
+ * wbinvd is a _very_ time consuming operation, so
+ * 1. wbinvd ... timer has a good possibility to expire while
+ *    irq disabled, it then would be delayed until
+ * 2. ... vmentry back to guest (and irq enalbed), timer interrupt
+ *    then occurs and drops guest at once;
+ * 3. drop to hypervisor ... then vmentry and wbinvd again;
+ *
+ * This loop will run again and again, until lucky enough wbinvd
+ * happens not to expire timer and then loop break, usually it would
+ * occur 10K~60K times, blocking guest 10s~60s.
+ *
+ * reprogram timer to avoid dead_like_loop.
+ */
+static inline void uc_wbinvd_and_timer_adjust(void)
+{
+    reprogram_timer(0);
+    wbinvd();
+    reprogram_timer(NOW() + MILLISECS(1));
+}
+
 void vmx_vmenter_helper(const struct cpu_user_regs *regs)
 {
     struct vcpu *curr = current;
@@ -2974,6 +2991,13 @@ void vmx_vmenter_helper(const struct cpu_user_regs *regs)
     struct hvm_vcpu_asid *p_asid;
     bool_t need_flush;
 
+    /*
+     * In case hypervisor may access hvm guest memory, and then
+     * cache line polluted under UC mode.
+     */
+    if ( unlikely(curr->arch.hvm_vcpu.cache_mode == NO_FILL_CACHE_MODE) )
+        uc_wbinvd_and_timer_adjust();
+
     if ( !cpu_has_vmx_vpid )
         goto out;
     if ( nestedhvm_vcpu_in_guestmode(curr) )
-- 
1.7.1

Attachment: 0001-VMX-wbinvd-when-vmentry-under-UC.patch
Description: 0001-VMX-wbinvd-when-vmentry-under-UC.patch

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