On Wed, 2022-06-08 at 09:47 +0200, Vitaly Kuznetsov wrote: > Maxim Levitsky <mlevitsk@xxxxxxxxxx> writes: > > > On Mon, 2022-06-06 at 10:36 +0200, Vitaly Kuznetsov wrote: > > > To allow flushing individual GVAs instead of always flushing the > > > whole > > > VPID a per-vCPU structure to pass the requests is needed. Use > > > standard > > > 'kfifo' to queue two types of entries: individual GVA (GFN + up to > > > 4095 > > > following GFNs in the lower 12 bits) and 'flush all'. > > > > Honestly I still don't think I understand why we can't just > > raise KVM_REQ_TLB_FLUSH_GUEST when the guest uses this interface > > to flush everthing, and then we won't need to touch the ring > > at all. > > The main reason is that we need to know what to flush: L1 or > L2. E.g. for VMX, KVM_REQ_TLB_FLUSH_GUEST is basically > > vpid_sync_context(vmx_get_current_vpid(vcpu)); > > which means that if the target vCPU transitions from L1 to L2 or vice > versa before KVM_REQ_TLB_FLUSH_GUEST gets processed we will flush the > wrong VPID. And actually the writer (the vCPU which processes the TLB > flush hypercall) is not anyhow synchronized with the reader (the vCPU > whose TLB needs to be flushed) here so we can't even know if the target > vCPU is in guest more or not. > > With the newly added KVM_REQ_HV_TLB_FLUSH, we always look at the > corresponding FIFO and process 'flush all' accordingly. In case the vCPU > switches between modes, we always raise KVM_REQ_HV_TLB_FLUSH request to > make sure we check. Note: we can't be raising KVM_REQ_TLB_FLUSH_GUEST > instead as it always means 'full tlb flush' and we certainly don't want > that. > OK, that makes sense! Let it be then. Best regards, Maxim Levitsky
