[Xen-devel] [PATCH v2 1/5] x86/boot: Initialise the debug registers correctly

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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

Move X86_DR6_DEFAULT into x86-defns.h along with the other architectural
register constants, and introduce a new X86_DR7_DEFAULT.  Use the existing
write_debugreg() helper, rather than opencoded inline assembly.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/cpu/common.c       | 12 ++++++++----
 xen/include/asm-x86/debugreg.h  |  2 --
 xen/include/asm-x86/x86-defns.h | 10 ++++++++++
 3 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 057859a..9d5bf66 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -3,6 +3,7 @@
 #include <xen/delay.h>
 #include <xen/smp.h>
 #include <asm/current.h>
+#include <asm/debugreg.h>
 #include <asm/processor.h>
 #include <asm/xstate.h>
 #include <asm/msr.h>
@@ -815,10 +816,13 @@ void cpu_init(void)
        /* Ensure FPU gets initialised for each domain. */
        stts();
 
-       /* Clear all 6 debug registers: */
-#define CD(register) asm volatile ( "mov %0,%%db" #register : : "r"(0UL) );
-       CD(0); CD(1); CD(2); CD(3); /* no db4 and db5 */; CD(6); CD(7);
-#undef CD
+       /* Reset debug registers: */
+       write_debugreg(0, 0);
+       write_debugreg(1, 0);
+       write_debugreg(2, 0);
+       write_debugreg(3, 0);
+       write_debugreg(6, X86_DR6_DEFAULT);
+       write_debugreg(7, X86_DR7_DEFAULT);
 }
 
 void cpu_uninit(unsigned int cpu)
diff --git a/xen/include/asm-x86/debugreg.h b/xen/include/asm-x86/debugreg.h
index b3b10ea..c57914e 100644
--- a/xen/include/asm-x86/debugreg.h
+++ b/xen/include/asm-x86/debugreg.h
@@ -24,8 +24,6 @@
 #define DR_STATUS_RESERVED_ZERO (~0xffffeffful) /* Reserved, read as zero */
 #define DR_STATUS_RESERVED_ONE  0xffff0ff0ul /* Reserved, read as one */
 
-#define X86_DR6_DEFAULT 0xffff0ff0ul    /* Default %dr6 value. */
-
 /* Now define a bunch of things for manipulating the control register.
    The top two bytes of the control register consist of 4 fields of 4
    bits - each field corresponds to one of the four debug registers,
diff --git a/xen/include/asm-x86/x86-defns.h b/xen/include/asm-x86/x86-defns.h
index 904041e..b80bbd8 100644
--- a/xen/include/asm-x86/x86-defns.h
+++ b/xen/include/asm-x86/x86-defns.h
@@ -97,4 +97,14 @@
 #define X86_XCR0_LWP_POS          62
 #define X86_XCR0_LWP              (1ULL << X86_XCR0_LWP_POS)
 
+/*
+ * Debug status flags in DR6.
+ */
+#define X86_DR6_DEFAULT         0xffff0ff0  /* Default %dr6 value. */
+
+/*
+ * Debug control flags in DR7.
+ */
+#define X86_DR7_DEFAULT         0x00000400  /* Default %dr7 value. */
+
 #endif /* __XEN_X86_DEFNS_H__ */
-- 
2.1.4


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