On Wed, Jul 05, 2023 at 12:53:58PM +0000, "Huang, Kai" <kai.huang@xxxxxxxxx> wrote: > On Wed, 2023-07-05 at 14:19 +0200, Peter Zijlstra wrote: > > On Wed, Jul 05, 2023 at 11:34:53AM +0000, Huang, Kai wrote: > > > > > Yeah I think from long-term's view, since SEAMCALLs to support live migration > > > pretty much uses all RCX/RDX/R8-R15 as input/output, it seems reasonable to > > > unify all of them, although I guess there might be some special handling to > > > VP.VMCALL and/or VP.ENTER, e.g., below: > > > > > > /* TDVMCALL leaf return code is in R10 */ > > > movq %r10, %rax > > > > > > So long-termly, I don't have objection to that. But my thinking is for the > > > first version of TDX host support, we don't have to support all SEAMCALLs but > > > only those involved in basic TDX support. > > > > Since those calls are out now, we should look at them now, there is no > > point in delaying the pain. That then gives us two options: > > > > - we accept them and their wonky calling convention and our code should > > be ready for it. > > > > - we reject them and send the TDX team a message to please try again > > but with a saner calling convention. > > > > Sticking our head in the sand and pretending like they don't exist isn't > > really a viable option at this point. > > OK. I'll work on this. > > But I think even we want to unify __tdx_module_call() and __tdx_hypercall(), the > first step should be making __tdx_module_call() look like __tdx_hypercall()? I > mean from organizing patchset's point of view, we cannot just do in one big > patch but need to split into small patches with each doing one thing. > > By thinking is perhaps we can organize this way: > > 1) Patch(es) to make TDX_MODULE_CALL macro / __tdx_module_call() look like > __tdx_hypercall(). > 2) Add SEAMCALL support based on TDX_MODULE_CALL, e.g., implement __seamcall(). > 3) Unify __tdx_module_call()/__seamcall() with __tdx_hypercall(). > > Does this look good? > > Btw, I've already part 1) based on your code, and sent the patches to Kirill for > review. Should I sent them out first? > > > > > > Also, the new SEAMCALLs to handle live migration all seem to have below > > > statement: > > > > > > AVX, AVX2 May be reset to the architectural INIT state > > > and > > > AVX512 > > > state > > > > > > Which means those SEAMCALLs need to preserve AVX* states too? > > > > Yes, we need to ensure the userspace 'FPU' state is saved before > > we call them. But I _think_ that KVM already does much of that. > > Let me look into this. KVM VCPU_RUN ioctl saves/restores FPU state by kvm_load_guest_fpu() and kvm_put_guest_fpu() which calls fpu_swap_kvm_fpstate(). Other KVM ioctls doesn't modify FPU. Because some SEAMCALLs related for live migration don't preserve FPU state, we need explicit save/restore of FPU state. -- Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
