Messages in this thread | | | Date | Wed, 5 Jan 2022 19:40:57 +0000 | From | Sean Christopherson <> | Subject | Re: [RFC PATCH 00/10] KVM: selftests: Add support for test-selectable ucall implementations |
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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.
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.
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