Messages in this thread | | | Subject | Re: [PATCH v4 6/6] KVM: VMX: enable IPI virtualization | From | Zeng Guang <> | Date | Sat, 18 Sep 2021 00:10:01 +0800 |
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On 9/11/2021 7:55 AM, Sean Christopherson wrote: > On Fri, Sep 10, 2021, Sean Christopherson wrote: >> On Mon, Aug 09, 2021, Zeng Guang wrote: >>> + if (!pages) >>> + return -ENOMEM; >>> + >>> + to_kvm_vmx(kvm)->pid_table = (void *)page_address(pages); >>> + to_kvm_vmx(kvm)->pid_last_index = KVM_MAX_VCPU_ID; >> I don't see the point of pid_last_index if we're hardcoding it to KVM_MAX_VCPU_ID. >> If I understand the ucode pseudocode, there's no performance hit in the happy >> case, i.e. it only guards against out-of-bounds accesses. >> >> And I wonder if we want to fail the build if this grows beyond an order-1 >> allocation, e.g. >> >> BUILD_BUG_ON(PID_TABLE_ORDER > 1); >> >> Allocating two pages per VM isn't terrible, but 4+ starts to get painful when >> considering the fact that most VMs aren't going to need more than one page. For >> now I agree the simplicity of not dynamically growing the table is worth burning >> a page. > Ugh, Paolo has queued a series which bumps KVM_MAX_VCPU_ID to 4096[*]. That makes > this an order-3 allocation, which is quite painful. One thought would be to let > userspace declare the max vCPU it wants to create, not sure if that would work for > xAPIC though. > > [*] https://lkml.kernel.org/r/1111efc8-b32f-bd50-2c0f-4c6f506b544b@redhat.com Thus we keep current design as no change.
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