[Xen-devel] [PATCH] fix for Failed VMEntry on VMX

[David Lively <dlively@xxxxxxxxxxxxxxx>]

I've been getting a "Failed VMEntry" when trying to boot a second
VMX guest (while the first one is still running, but is no longer in
real mode).  This patch fixes it.

VMX(assist) uses vm86 in its real mode emulation.  Upon vmentry
into a guest in vm86 mode, all segment bases must be equal to the
corresponding segment selector shifted left four bits.  The vmx
routine vmx_load_cpu_guest_regs() was loading the segment
selectors.  Now it makes sure to set the segment bases appropriately
if we're in vm86 mode.

Tested on 64bit hypervisor with 2 64-bit VMX domUs (on
2-way dom0).

Dave

Ensure segment bases are consistent with their
selectors for VMX guests in VM86 mode.

Signed-off-by: David Lively <dlively@xxxxxxxxxxxxxxx>

diff -r 880433ba7487 xen/arch/x86/hvm/vmx/vmx.c
--- a/xen/arch/x86/hvm/vmx/vmx.c        Mon May  1 17:08:02 2006 -0400
+++ b/xen/arch/x86/hvm/vmx/vmx.c        Tue May  2 10:31:03 2006 -0400
@@ -487,6 +487,33 @@ static void vmx_store_cpu_guest_regs(
         __vmptrld(virt_to_maddr(current->arch.hvm_vmx.vmcs));
 }
 
+/* Ensure segment bases are consistent with their
+ * selectors for guests in VM86 mode.
+ */
+static void fixup_vm86_seg_bases(struct cpu_user_regs *regs)
+{
+    unsigned long base;
+
+    BUG_ON(__vmread(GUEST_ES_BASE, &base));
+    if (regs->es << 4 != base)
+        BUG_ON(__vmwrite(GUEST_ES_BASE, regs->es << 4));
+    BUG_ON(__vmread(GUEST_CS_BASE, &base));
+    if (regs->cs << 4 != base)
+        BUG_ON(__vmwrite(GUEST_CS_BASE, regs->cs << 4));
+    BUG_ON(__vmread(GUEST_SS_BASE, &base));
+    if (regs->ss << 4 != base)
+        BUG_ON(__vmwrite(GUEST_SS_BASE, regs->ss << 4));
+    BUG_ON(__vmread(GUEST_DS_BASE, &base));
+    if (regs->ds << 4 != base)
+        BUG_ON(__vmwrite(GUEST_DS_BASE, regs->ds << 4));
+    BUG_ON(__vmread(GUEST_FS_BASE, &base));
+    if (regs->fs << 4 != base)
+        BUG_ON(__vmwrite(GUEST_FS_BASE, regs->fs << 4));
+    BUG_ON(__vmread(GUEST_GS_BASE, &base));
+    if (regs->gs << 4 != base)
+        BUG_ON(__vmwrite(GUEST_GS_BASE, regs->gs << 4));
+}
+
 void vmx_load_cpu_guest_regs(struct vcpu *v, struct cpu_user_regs *regs)
 {
     if ( v != current )
@@ -523,6 +550,8 @@ void vmx_load_cpu_guest_regs(struct vcpu
         __vm_set_bit(EXCEPTION_BITMAP, EXCEPTION_BITMAP_DB);
     else
         __vm_clear_bit(EXCEPTION_BITMAP, EXCEPTION_BITMAP_DB);
+    if (regs->rflags & EF_VM)
+        fixup_vm86_seg_bases(regs);
 
     __vmwrite(GUEST_CS_SELECTOR, regs->cs);
     __vmwrite(GUEST_RIP, regs->rip);
@@ -540,6 +569,8 @@ void vmx_load_cpu_guest_regs(struct vcpu
         __vm_set_bit(EXCEPTION_BITMAP, EXCEPTION_BITMAP_DB);
     else
         __vm_clear_bit(EXCEPTION_BITMAP, EXCEPTION_BITMAP_DB);
+    if (regs->eflags & EF_VM)
+        fixup_vm86_seg_bases(regs);
 
     __vmwrite(GUEST_CS_SELECTOR, regs->cs);
     __vmwrite(GUEST_RIP, regs->eip);

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