On Wed, Feb 27, 2019 at 10:55:46PM +0800, Kairui Song wrote: > On Wed, Feb 27, 2019 at 8:02 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > On Tue, Feb 26, 2019 at 11:56:15PM +0800, Kairui Song wrote: > > > arch/x86/hyperv/hv_init.c | 4 ++++ > > > 1 file changed, 4 insertions(+) > > > > > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > > > index 7abb09e2eeb8..92291c18d716 100644 > > > --- a/arch/x86/hyperv/hv_init.c > > > +++ b/arch/x86/hyperv/hv_init.c > > > @@ -406,6 +406,10 @@ void hyperv_cleanup(void) > > > /* Reset our OS id */ > > > wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0); > > > > > > + /* Cleanup page reference before reset the page */ > > > + hv_hypercall_pg = NULL; > > > + wmb(); > > > > What do we need that SFENCE for? Any why does it lack a comment? > > Hi, that's for ensuring the hv_hypercall_pg is reset to NULL before > the following wrmsr call. The wrmsr call will make the pointer address > invalid. WRMSR is a serializing instruction (except for TSC_DEADLINE and the X2APIC). > I can add some comment in V2 if this is OK. Barriers must always have a comment. _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
