Re: [patch 4/8] MDS basics 4

On Tue, 19 Feb 2019, speck for Thomas Gleixner wrote:
> On Tue, 19 Feb 2019, speck for Andrew Cooper wrote:
> 
> > On 19/02/2019 12:44, speck for Thomas Gleixner wrote:
> > > Subject: [patch 4/8] x86/speculation/mds: Conditionaly clear CPU buffers on idle entry
> > > From: Thomas Gleixner <[email protected]>
> > >
> > > Add a static key which controls the invocation of the CPU buffer clear
> > > mechanism on idle entry. This is independent of other MDS mitigations
> > > because the idle entry invocation to mitigate the potential leakage due to
> > > store buffer repartitioning is only necessary on SMT systems.
> > >
> > > Add the actual invocations to the different halt/mwait variants which
> > > covers all usage sites. mwaitx is not patched as it's not available on
> > > Intel CPUs.
> > >
> > > Signed-off-by: Thomas Gleixner <[email protected]>
> > 
> > Unfortunately, clearing is needed on the exit from idle as well as the
> > entry.
> > 
> > This only impacts the store buffer (MSBDS, previously PSF) because it
> > gets statically re-partitioned when a thread comes in and out of idle.
> > 
> > >From the point of view of the thread going idle, when going idle my half
> > of the store buffers get given to the other thread and potentially leak
> > my secrets, whereas when coming out of idle, the other threads store
> > buffers get split with me, potentially leaking their secrets.
> 
> Duh, indeed. Easy enough to fix.

Delta patch below. Stupid me even mentioned the repartioning on both sides
in the changelog.

Thanks,
 
	tglx

8<------------------
--- a/arch/x86/include/asm/irqflags.h
+++ b/arch/x86/include/asm/irqflags.h
@@ -58,12 +58,14 @@ static inline __cpuidle void native_safe
 {
 	mds_clear_cpu_buffers(&idle_mds_clear_cpu_buffers);
 	asm volatile("sti; hlt": : :"memory");
+	mds_clear_cpu_buffers(&idle_mds_clear_cpu_buffers);
 }
 
 static inline __cpuidle void native_halt(void)
 {
 	mds_clear_cpu_buffers(&idle_mds_clear_cpu_buffers);
 	asm volatile("hlt": : :"memory");
+	mds_clear_cpu_buffers(&idle_mds_clear_cpu_buffers);
 }
 
 #endif
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -46,6 +46,8 @@ static inline void __mwait(unsigned long
 	/* "mwait %eax, %ecx;" */
 	asm volatile(".byte 0x0f, 0x01, 0xc9;"
 		     :: "a" (eax), "c" (ecx));
+
+	mds_clear_cpu_buffers(&idle_mds_clear_cpu_buffers);
 }
 
 /*