On Tue, May 01, 2018 at 08:30:27PM +0200, speck for Thomas Gleixner wrote:
> On Tue, 1 May 2018, speck for Konrad Rzeszutek Wilk wrote:
> > 
> > On my Skylake box this does what is expected:
> > 
> > And I don't see the weird issue that Tim reported?
> 
> That depends on your ucode loading mechanism.

Oooh <duh>. Right, that would explain it:
RHEL-64 <opc@instance-20180426-1449:~> dmesg | grep micro
[    0.000000] microcode: microcode updated early to revision 0x200004a, date = 2018-03-28
[   28.499014] microcode: sig=0x50654, pf=0x80, revision=0x200004a
[   28.575504] microcode: Microcode Update Driver: v2.2.
> 
> > RHEL-64 <root@instance-20180426-1449:/home/opc> ./test-prctl
> 
> Could you please send that test thing around? It's trivial enough but I'm a
> lousy user space programmer and lazy :)

It is very umm, crappy but sure - see inline and attached. And it does not
do any ASSERTS or such to verify things. And I've no clue why the tabs all
changed to spaces.


#include <stdio.h>
       #include <sys/prctl.h>

#define SPEC_CTRL_RDS_SHIFT            2          /* Reduced Data Speculation bit */
/* Per task speculation control */
#define PR_SET_SPECULATION_CTRL                52
#define PR_GET_SPECULATION_CTRL                53
/* Speculation control variants */
# define PR_SPEC_STORE_BYPASS          0
/* Return and control values for PR_SET/GET_SPECULATION_CTRL */
# define PR_SPEC_NOT_AFFECTED          0
# define PR_SPEC_PRCTL                 (1UL << 0)
# define PR_SPEC_ENABLE                        (1UL << 1)
# define PR_SPEC_DISABLE               (1UL << 2)

void print_bitfields(int r)
{
 if ( r >= 0 )
 	fprintf(stderr, "	r=%s %s %s\n", r & PR_SPEC_PRCTL ? "PR_SPEC_PRCTL" : "",
		r & PR_SPEC_ENABLE ? "PR_SPEC_ENABLE" : "",
		r & PR_SPEC_DISABLE ? "PR_SPEC_DISABLE" : "");

}
void get_v(void)
{
 int r;
 r = prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, NULL, NULL,NULL);
 fprintf(stderr, "   PR_GET_SPECULATION_CTRL PR_SPEC_STORE_BYPASS r=%d\n", r);
 print_bitfields(r);

}

int main(void)
{
 int r;

 fprintf(stderr,"Initial state\n"); 
 get_v();

 r = prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, NULL, NULL);
 fprintf(stderr, "PR_SET_SPECULATION_CTRL PR_SPEC_DISABLE r=%d\n", r);
 print_bitfields(r);
 get_v();

 /* Two DISALBE in a row*/
 r = prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, NULL, NULL);
 fprintf(stderr, "PR_SET_SPECULATION_CTRL PR_SPEC_DISABLE r=%d\n", r);
 print_bitfields(r);
 get_v();

 /* Two enable in a row. */
 r = prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, NULL, NULL);
 fprintf(stderr, "PR_SET_SPECULATION_CTRL PR_SPEC_ENABLE r=%d\n", r);
 print_bitfields(r);
 get_v();

 r = prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_ENABLE, NULL, NULL);
 fprintf(stderr, "PR_SET_SPECULATION_CTRL PR_SPEC_ENABLE r=%d\n", r);
 print_bitfields(r);
 get_v();
 fprintf(stderr,"\nReal test-case\n");
 /* The real normal test-case */
 r = prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_STORE_BYPASS, PR_SPEC_DISABLE, NULL, NULL);
 fprintf(stderr, "PR_SET_SPECULATION_CTRL PR_SPEC_DISABLE r=%d\n", r);
 print_bitfields(r);
 get_v();

 do { } while (1);
 
	return 0;
}

> 
> Thanks,
> 
> 	tglx