tools/dombuilder: Initialise vcpu debug registers correctly

In particular, initialising %dr6 with the value 0 is buggy, because on
hardware supporting Transactional Memory, it will cause the sticky RTM bit to
be asserted, even though a debug exception from a transaction hasn't actually
been observed.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
master commit: 46029da12e5efeca6d957e5793bd34f2965fa0a1
master date: 2018-10-24 14:43:05 +0100

diff --git a/tools/libxc/xc_dom_x86.c b/tools/libxc/xc_dom_x86.c
index e33a28847da678b45f8bfccadaae033257124f8e..3ab918ca821e47c0bc7cd440a4bc576e97a891cd 100644 (file)
--- a/tools/libxc/xc_dom_x86.c
+++ b/tools/libxc/xc_dom_x86.c
@@ -53,6 +53,9 @@
 #define X86_CR0_PE 0x01
 #define X86_CR0_ET 0x10
 
+#define X86_DR6_DEFAULT 0xffff0ff0u
+#define X86_DR7_DEFAULT 0x00000400u
+
 #define SPECIALPAGE_PAGING   0
 #define SPECIALPAGE_ACCESS   1
 #define SPECIALPAGE_SHARING  2
@@ -860,6 +863,9 @@ static int vcpu_x86_32(struct xc_dom_image *dom)
         dom->parms.virt_base + (dom->start_info_pfn) * PAGE_SIZE_X86;
     ctxt->user_regs.eflags = 1 << 9; /* Interrupt Enable */
 
+    ctxt->debugreg[6] = X86_DR6_DEFAULT;
+    ctxt->debugreg[7] = X86_DR7_DEFAULT;
+
     ctxt->flags = VGCF_in_kernel_X86_32 | VGCF_online_X86_32;
     if ( dom->parms.pae == XEN_PAE_EXTCR3 ||
          dom->parms.pae == XEN_PAE_BIMODAL )
@@ -907,6 +913,9 @@ static int vcpu_x86_64(struct xc_dom_image *dom)
         dom->parms.virt_base + (dom->start_info_pfn) * PAGE_SIZE_X86;
     ctxt->user_regs.rflags = 1 << 9; /* Interrupt Enable */
 
+    ctxt->debugreg[6] = X86_DR6_DEFAULT;
+    ctxt->debugreg[7] = X86_DR7_DEFAULT;
+
     ctxt->flags = VGCF_in_kernel_X86_64 | VGCF_online_X86_64;
     cr3_pfn = xc_dom_p2m(dom, dom->pgtables_seg.pfn);
     ctxt->ctrlreg[3] = xen_pfn_to_cr3_x86_64(cr3_pfn);
@@ -1011,6 +1020,9 @@ static int vcpu_hvm(struct xc_dom_image *dom)
     /* Set the IP. */
     bsp_ctx.cpu.rip = dom->parms.phys_entry;
 
+    bsp_ctx.cpu.dr6 = X86_DR6_DEFAULT;
+    bsp_ctx.cpu.dr7 = X86_DR7_DEFAULT;
+
     if ( dom->start_info_seg.pfn )
         bsp_ctx.cpu.rbx = dom->start_info_seg.pfn << PAGE_SHIFT;