Re: [RFC PATCH 00/10] KVM: selftests: Add support for test-selectable ucall implementations

From: Sean Christopherson <seanjc@google.com>
To: Michael Roth <michael.roth@amd.com>
Cc: Brijesh Singh <brijesh.singh@amd.com>,
	kvm@vger.kernel.org, David Hildenbrand <david@redhat.com>,
	Marc Orr <marcorr@google.com>,
	linux-kselftest@vger.kernel.org,
	"H . Peter Anvin" <hpa@zytor.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Shuah Khan <shuah@kernel.org>,
	kvmarm@lists.cs.columbia.edu, Nathan Tempelman <natet@google.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Marc Zyngier <maz@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	x86@kernel.org, Ingo Molnar <mingo@redhat.com>,
	Mingwei Zhang <mizhang@google.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Borislav Petkov <bp@alien8.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Varad Gautam <varad.gautam@suse.com>,
	Jim Mattson <jmattson@google.com>,
	Steve Rutherford <srutherford@google.com>,
	linux-kernel@vger.kernel.org,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	David Woodhouse <dwmw@amazon.co.uk>
Subject: Re: [RFC PATCH 00/10] KVM: selftests: Add support for test-selectable ucall implementations
Date: Wed, 5 Jan 2022 22:02:53 +0000	[thread overview]
Message-ID: <YdYVjfMqf+GjsU+p@google.com> (raw)
In-Reply-To: <20220105213519.g746jzf756nax562@amd.com>

On Wed, Jan 05, 2022, Michael Roth wrote:
> On Wed, Jan 05, 2022 at 07:40:57PM +0000, Sean Christopherson wrote:
> > 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)

I don't think we want to do this here, but instead down in the arch-specific
ucall_init().  Also, not sure if I was clear before (can't tell what you interpreted
based on the above snippet), but I think we'll want VM_MODE_SEV etc... to be
modifiers on top of the VA/PA stuff.

>   	    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?

Nope, all yours.  Thanks!
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