From: Michael Roth <michael.roth@amd.com>
To: Sean Christopherson <seanjc@google.com>
Cc: <linux-kselftest@vger.kernel.org>, <kvm@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <x86@kernel.org>,
Nathan Tempelman <natet@google.com>,
Marc Orr <marcorr@google.com>,
Steve Rutherford <srutherford@google.com>,
Mingwei Zhang <mizhang@google.com>,
Brijesh Singh <brijesh.singh@amd.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
Varad Gautam <varad.gautam@suse.com>,
Shuah Khan <shuah@kernel.org>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
David Woodhouse <dwmw@amazon.co.uk>,
Ricardo Koller <ricarkol@google.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
"Janosch Frank" <frankja@linux.ibm.com>,
David Hildenbrand <david@redhat.com>,
"Claudio Imbrenda" <imbrenda@linux.ibm.com>,
Marc Zyngier <maz@kernel.org>, James Morse <james.morse@arm.com>,
Alexandru Elisei <alexandru.elisei@arm.com>,
"Suzuki K Poulose" <suzuki.poulose@arm.com>,
<kvmarm@lists.cs.columbia.edu>
Subject: Re: [RFC PATCH 00/10] KVM: selftests: Add support for test-selectable ucall implementations
Date: Wed, 5 Jan 2022 15:35:19 -0600 [thread overview]
Message-ID: <20220105213519.g746jzf756nax562@amd.com> (raw)
In-Reply-To: <YdX0SRoBXReggrVA@google.com>
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?
next prev parent reply other threads:[~2022-01-05 21:35 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 16:46 [RFC PATCH 00/10] KVM: selftests: Add support for test-selectable ucall implementations Michael Roth
2021-12-10 16:46 ` [PATCH RFC 01/10] kvm: selftests: move base kvm_util.h declarations to kvm_util_base.h Michael Roth
2021-12-10 16:46 ` [PATCH RFC 02/10] kvm: selftests: move ucall declarations into ucall_common.h Michael Roth
2021-12-25 9:11 ` Andrew Jones
2021-12-10 16:46 ` [PATCH RFC 03/10] kvm: selftests: introduce ucall_ops for test/arch-specific ucall implementations Michael Roth
2021-12-10 16:46 ` [PATCH RFC 04/10] kvm: arm64: selftests: use ucall_ops to define default ucall implementation Michael Roth
2021-12-10 16:46 ` [PATCH RFC 05/10] kvm: s390: " Michael Roth
2021-12-10 16:46 ` [PATCH RFC 06/10] kvm: selftests: add ucall interfaces based around shared memory Michael Roth
2021-12-10 16:46 ` [PATCH RFC 07/10] kvm: selftests: add ucall_shared ops for PIO Michael Roth
2021-12-10 16:46 ` [PATCH RFC 08/10] kvm: selftests: introduce ucall implementation based on halt instructions Michael Roth
2021-12-10 16:46 ` [PATCH RFC 09/10] kvm: selftests: add GUEST_SHARED_* macros for shared ucall implementations Michael Roth
2021-12-10 16:46 ` [PATCH RFC 10/10] kvm: selftests: add ucall_test to test various ucall functionality Michael Roth
2021-12-22 14:46 ` [RFC PATCH 00/10] KVM: selftests: Add support for test-selectable ucall implementations Paolo Bonzini
2021-12-30 21:11 ` Sean Christopherson
2022-01-04 23:35 ` Michael Roth
2022-01-05 0:17 ` Sean Christopherson
2022-01-05 17:02 ` Michael Roth
2022-01-05 17:43 ` Sean Christopherson
2022-01-05 19:11 ` Michael Roth
2022-01-05 19:40 ` Sean Christopherson
2022-01-05 21:35 ` Michael Roth [this message]
2022-01-05 22:02 ` Sean Christopherson
2022-01-05 22:32 ` Michael Roth
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