On 03.05.2022 10:26, Roger Pau Monne wrote: > Expose VIRT_SSBD to guests if the hardware supports setting SSBD in > the LS_CFG MSR (a.k.a. non-architectural way). Different AMD CPU > families use different bits in LS_CFG, so exposing VIRT_SPEC_CTRL.SSBD > allows for an unified way of exposing SSBD support to guests on AMD > hardware that's compatible migration wise, regardless of what > underlying mechanism is used to set SSBD. > > Note that on AMD Family 17h and Hygon Family 18h processors the value > of SSBD in LS_CFG is shared between threads on the same core, so > there's extra logic in order to synchronize the value and have SSBD > set as long as one of the threads in the core requires it to be set. > Such logic also requires extra storage for each thread state, which is > allocated at initialization time. > > Do the context switching of the SSBD selection in LS_CFG between > hypervisor and guest in the same handler that's already used to switch > the value of VIRT_SPEC_CTRL. > > Suggested-by: Andrew Cooper <[email protected]> > Signed-off-by: Roger Pau Monné <[email protected]>
Reviewed-by: Jan Beulich <[email protected]> with one nit: > +void amd_set_legacy_ssbd(bool enable) > +{ > + const struct cpuinfo_x86 *c = ¤t_cpu_data; > + struct ssbd_ls_cfg *status; > + > + if ((c->x86 != 0x17 && c->x86 != 0x18) || c->x86_num_siblings <= 1) { > + set_legacy_ssbd(c, enable); > + return; > + } > + > + status = &ssbd_ls_cfg[c->phys_proc_id * ssbd_max_cores + > + c->cpu_core_id]; > + > + /* > + * Open code a very simple spinlock: this function is used with GIF==0 > + * and different IF values, so would trigger the checklock detector. > + * Instead of trying to workaround the detector, use a very simple lock > + * implementation: it's better to reduce the amount of code executed > + * with GIF==0. > + */ > + while ( test_and_set_bool(status->locked) ) Nit: A bit of Xen style slipped into here. > --- a/xen/arch/x86/hvm/svm/svm.c > +++ b/xen/arch/x86/hvm/svm/svm.c > @@ -3126,6 +3126,8 @@ void vmexit_virt_spec_ctrl(void) > > if ( cpu_has_virt_ssbd ) > wrmsr(MSR_VIRT_SPEC_CTRL, val, 0); > + else > + amd_set_legacy_ssbd(val); > } > > /* Called with GIF=0. */ > @@ -3138,6 +3140,8 @@ void vmentry_virt_spec_ctrl(void) > > if ( cpu_has_virt_ssbd ) > wrmsr(MSR_VIRT_SPEC_CTRL, current->arch.msrs->virt_spec_ctrl.raw, 0); > + else > + amd_set_legacy_ssbd(!val); > } Aiui the adjustment suggested for patch 2 will not really get in the way of this, by only requiring to drop the ! . Jan
