Messages in this thread | | | Date | Wed, 13 Mar 2024 09:32:06 -0500 | Subject | Re: [PATCH v2] KVM:SVM: Flush cache only on CPUs running SEV guest | From | Tom Lendacky <> |
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On 3/12/24 09:45, Tom Lendacky wrote: > On 3/6/24 20:14, Zheyun Shen wrote: >> On AMD CPUs without ensuring cache consistency, each memory page >> reclamation in an SEV guest triggers a call to wbinvd_on_all_cpus(), >> thereby affecting the performance of other programs on the host. >> >> Typically, an AMD server may have 128 cores or more, while the SEV guest >> might only utilize 8 of these cores. Meanwhile, host can use qemu-affinity >> to bind these 8 vCPUs to specific physical CPUs. >> >> Therefore, keeping a record of the physical core numbers each time a vCPU >> runs can help avoid flushing the cache for all CPUs every time. >> >> Since the usage of sev_flush_asids() isn't tied to a single VM, we just >> replace all wbinvd_on_all_cpus() with sev_do_wbinvd() except for that >> in sev_flush_asids(). >> >> Signed-off-by: Zheyun Shen <szy0127@sjtu.edu.cn> > > I'm unable to launch my SEV or SEV-ES guests with this patch (haven't > tried an SEV-SNP guest, yet). Qemu segfaults at launch. > > I'll try to dig into what is happening, but not sure when I'll be able to > do that at the moment.
Looks like it's the use of get_cpu() without an associated put_cpu() when setting the cpumask. I think what you really want to use is just the cpu parameter that is passed into pre_sev_run().
>
>> void sev_free_vcpu(struct kvm_vcpu *vcpu) >> @@ -2648,6 +2666,7 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu) >> sd->sev_vmcbs[asid] = svm->vmcb; >> svm->vmcb->control.tlb_ctl = TLB_CONTROL_FLUSH_ASID; >> vmcb_mark_dirty(svm->vmcb, VMCB_ASID); >> + cpumask_set_cpu(get_cpu(), sev_get_wbinvd_dirty_mask(svm->vcpu.kvm));
Just use 'cpu' here.... ^
When I do that I'm able to boot an SEV and SEV-ES guest.
I'll wait for the next version, in case there are other changes, before running through our CI for more thorough testing than just a single boot.
Thanks, Tom
>> } >> #define GHCB_SCRATCH_AREA_LIMIT (16ULL * PAGE_SIZE)
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