On Wed, Jan 05, 2022 at 07:40:57PM +0000, Sean Christopherson wrote:
> On Wed, Jan 05, 2022, Michael Roth wrote:
> > On Wed, Jan 05, 2022 at 05:43:21PM +0000, Sean Christopherson wrote:
> > > Because it uses multiple VMs, and my rough sketch only allows for a single VM to
> > > use ucall. Though I suppose we could simply keep appending to the ucall list for
> > > every VM. The requirement would then be that all VMs are of the same type, i.e.
> > > utilize the same ucall_ops.
> >
> > Hmm, maybe I misread your patch. Not supporting multiple VMs was the
> > reason I gave up on having the ucall structs allocated on-demand and
> > went with requiring them to be passed as arguments to ucall().
> >
> > I thought with your patch you had solved that by having each vm have it's
> > own pool, via vm->ucall_list, and then mapping each pool into each guest
> > separately via:
> >
> > ucall_init(vm):
> > ucall_list = vm->ucall_list
> > sync_global_to_guest(ucall_list).
> >
> > then as long as that ucall_init() is done *after* the guest calls
> > kvm_vm_elf_load(), it will end up with a 'ucall_list' global that points
> > to it's own specific vm->ucall_list. Then on the test side it doesn't
> > matter what the 'ucall_list' global is currently set to since you have
> > the GPA and know what vm exited.
> >
> > Or am I missing something there?
>
> Ha, that was not at all intented. But yes, it should work. I'd rather be lucky
> than good?
:)
>
> > Although even if that is the case, now that we're proposing doing the
> > ucall_init() inside vm_create(), then we run the risk of a test calling
> > kvm_vm_elf_load() after, which might clobber the guest's copy of
> > ucall_list global if ucall_init() had since been called for another VM.
> > But that could maybe be worked around by having whatever vm_create()
> > variant we use also do the kvm_vm_elf_load() unconditionally as part of
> > creation.
>
> Will sync_global_to_guest() even work as intended if kvm_vm_elf_load() hasn't
> been called? If not, then sync_global_{to,from}_guest() should really assert if
> the test hasn't been loaded.
Yah, seems like it would get clobbered by kvm_vm_elf_load() later. And
can't think of any good reason to use sync_global_to_guest() without also
needing kvm_vm_elf_load() at some point, so makes sense to enforce it.
>
> As for ucall_init(), I think the best approach would be to make kvm_vm_elf_load()
> a static and replace all calls with:
>
> kvm_vm_load_guest(vm);
>
> where its implementation is:
>
> void kvm_vm_load_guest(struct kvm_vm *vm)
> {
> kvm_vm_elf_load(vm, program_invocation_name);
>
> ucall_init(vm);
> }
>
> The logic being that if a test creates a VM but never loads any code into the guest,
> e.g. kvm_create_max_vcpus, then it _can't_ make ucalls.
Makes sense. And if different ops are needed for vmgexit()/tdcall() it
could be something like (if based on patches 1-5 of this series, and
extending vm_guest_mode as you suggested earlier):
void kvm_vm_load_guest(struct kvm_vm *vm)
{
kvm_vm_elf_load(vm, program_invocation_name);
if (vm->mode == VM_MODE_SEV)
ucall_init_ops(vm, ucall_ops_pio_vmgexit);
else (vm->vm_type == VM_MODE_TDX)
ucall_init_ops(vm, ucall_ops_pio_tdcall);
else
ucall_init_ops(vm, ucall_ops_pio);
Shame we have to update all the kvm_vm_elf_load() call-sites, but
they'd end up potentially breaking things if left as-is anyway.
Were you planning on sending patches for these changes, or should I incorporate
your prototype and take a stab at the other changes as part of v2 of this
series?
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