On 14/05/18 16:48, Wei Liu wrote: > On Fri, May 11, 2018 at 11:38:14AM +0100, Andrew Cooper wrote: >> If Xen is virtualising MSR_SPEC_CTRL handling for guests, but using 0 as its >> own MSR_SPEC_CTRL value, spec_ctrl_{enter,exit}_idle() need not write to the >> MSR. >> >> Requested-by: Jan Beulich <jbeul...@suse.com> >> Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> >> --- >> CC: Jan Beulich <jbeul...@suse.com> >> CC: Wei Liu <wei.l...@citrix.com> >> CC: Roger Pau Monné <roger....@citrix.com> >> CC: Juergen Gross <jgr...@suse.com> >> --- >> xen/arch/x86/spec_ctrl.c | 4 ++++ >> xen/include/asm-x86/cpufeatures.h | 1 + >> xen/include/asm-x86/spec_ctrl.h | 8 ++------ >> 3 files changed, 7 insertions(+), 6 deletions(-) >> >> diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c >> index a2328bd..f4a3165 100644 >> --- a/xen/arch/x86/spec_ctrl.c >> +++ b/xen/arch/x86/spec_ctrl.c >> @@ -526,6 +526,10 @@ void __init init_speculation_mitigations(void) >> /* (Re)init BSP state now that default_spec_ctrl_flags has been >> calculated. */ >> init_shadow_spec_ctrl_state(); >> >> + /* If Xen is using any MSR_SPEC_CTRL settings, adjust the idle path. */ >> + if ( default_xen_spec_ctrl ) >> + setup_force_cpu_cap(X86_FEATURE_SC_MSR_IDLE); >> + >> xpti_init_default(false); >> if ( opt_xpti == 0 ) >> setup_force_cpu_cap(X86_FEATURE_NO_XPTI); >> diff --git a/xen/include/asm-x86/cpufeatures.h >> b/xen/include/asm-x86/cpufeatures.h >> index 9d5d81e..b90aa2d 100644 >> --- a/xen/include/asm-x86/cpufeatures.h >> +++ b/xen/include/asm-x86/cpufeatures.h >> @@ -31,3 +31,4 @@ XEN_CPUFEATURE(SC_MSR_HVM, (FSCAPINTS+0)*32+17) /* >> MSR_SPEC_CTRL used by Xe >> XEN_CPUFEATURE(SC_RSB_PV, (FSCAPINTS+0)*32+18) /* RSB overwrite >> needed for PV */ >> XEN_CPUFEATURE(SC_RSB_HVM, (FSCAPINTS+0)*32+19) /* RSB overwrite >> needed for HVM */ >> XEN_CPUFEATURE(NO_XPTI, (FSCAPINTS+0)*32+20) /* XPTI mitigation not >> in use */ >> +XEN_CPUFEATURE(SC_MSR_IDLE, (FSCAPINTS+0)*32+21) /* (SC_MSR_PV || >> SC_MSR_HVM) && default_xen_spec_ctrl */ > I don't follow: the code above only depends on default_xen_spec_ctrl but > the comment says SC_MSR_PV and SC_MSR_HVM are also taken into > consideration.
default_xen_spec_ctrl is only ever nonzero when SC_MSR_PV or SC_MSR_HVM is set. In principle, I could assert that one of the two is set. I have phrased it like this because it is going to become rather more complicated (than != 0) when adding IBRS_ATT mode. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel