Messages in this thread | | | Date | Fri, 26 Nov 2021 08:56:59 +0100 | Subject | Re: [RFC PATCH v3 54/59] KVM: X86: Introduce initial_tsc_khz in struct kvm_arch | From | Paolo Bonzini <> |
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On 11/26/21 00:26, Thomas Gleixner wrote: > Paolo, > > On Thu, Nov 25 2021 at 23:13, Paolo Bonzini wrote: >> On 11/25/21 22:05, Thomas Gleixner wrote: >> If there are some patches that are actually independent, go ahead and >> submit them early. But more practically, for the bulk of the changes >> what you need to do is: >> >> 1) incorporate into patch 55 a version of tdx.c that essentially does >> KVM_BUG_ON or WARN_ON for each function. Temporarily keep the same huge >> patch that adds the remaining 2000 lines of tdx.c > > There is absolutely no reason to populate anything upfront at all. > Why? > > Simply because that whole muck cannot work until all pieces are in place.
It can, sort of. It cannot run a complete guest, but it could in principle run a toy guest with a custom userspace, like the ones that make up tools/testing/selftests/kvm. (Note that KVM_BUG_ON marks the VM as bugged but doesn't hang the whole machine).
AMD was working on infrastructure to do this for SEV and SEV-ES.
> So why would you provide: > > handle_A(...) { BUG(); } > .. > handle_Z(...) { BUG(); } > > with all the invocations in the common emulation dispatcher: > > handle_stuff(reason) > { > switch(reason) { > case A: return handle_A(); > ... > case Z: return handle_Z(); > default: BUG(); > } > };
If it's a switch statement that's good, but the common case is more similar to this:
vmx_handle_A(...) { ... } +tdx_handle_A(...) { ... } + +vt_handle_A(...) { + if (is_tdx(vcpu->kvm)) + tdx_handle_A(...); + else + vmx_handle_A(...); +}
...
- .handle_A = vmx_handle_A, + .handle_A = vt_handle_A,
And you could indeed do it in a single patch, without adding the stub tdx_handle_A upfront. But you would have code that is broken and who knows what the effects would be of calling vmx_handle_A on a TDX virtual machine. It could be an error, or it could be memory corruption.
> In both scenarious you cannot boot a TDX guest until you reached $Z, but > in the gradual one you and the reviewers have the pleasure of looking at > one thing at a time.
I think both of them are gradual. Not having the stubs might be a little more gradual, but it is a very minor issue for the reviewability of the whole thing.
Paolo
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