[PATCH v1 2/3] x86/xen/msr: Fix uninitialized symbol 'err'

["Xin Li (Intel)" <xin@xxxxxxxxx>]

xen_read_msr_safe() currently passes an uninitialized argument err to
xen_do_read_msr().  But as xen_do_read_msr() may not set the argument,
xen_read_msr_safe() could return err with an unpredictable value.

To ensure correctness, initialize err to 0 (representing success)
in xen_read_msr_safe().

Because xen_read_msr_safe() is essentially a wrapper of xen_do_read_msr(),
the latter should be responsible for initializing the value of *err to 0.
Thus initialize *err to 0 in xen_do_read_msr().

Fixes: 502ad6e5a619 ("x86/msr: Change the function type of 
native_read_msr_safe()")
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://lore.kernel.org/xen-devel/aBxNI_Q0-MhtBSZG@stanley.mountain/
Signed-off-by: Xin Li (Intel) <xin@xxxxxxxxx>
---
 arch/x86/xen/enlighten_pv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 3be38350f044..01f1d441347e 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1091,6 +1091,9 @@ static u64 xen_do_read_msr(u32 msr, int *err)
 {
        u64 val = 0;    /* Avoid uninitialized value for safe variant. */
 
+       if (err)
+               *err = 0;
+
        if (pmu_msr_chk_emulated(msr, &val, true))
                return val;
 
@@ -1162,7 +1165,7 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
 
 static int xen_read_msr_safe(u32 msr, u64 *val)
 {
-       int err;
+       int err = 0;
 
        *val = xen_do_read_msr(msr, &err);
        return err;
-- 
2.49.0