linux-kernel - Re: [PATCH V2 1/1] KVM: TDX: Add sub-ioctl KVM_TDX_TERMINATE

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Message-ID: <0a175c77-9911-47a4-ad4e-8bed07fb9cf4@intel.com>
Date: Tue, 22 Apr 2025 10:30:12 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Vishal Annapurve
	<vannapurve@...gle.com>
CC: <pbonzini@...hat.com>, <mlevitsk@...hat.com>, <kvm@...r.kernel.org>,
	<rick.p.edgecombe@...el.com>, <kirill.shutemov@...ux.intel.com>,
	<kai.huang@...el.com>, <reinette.chatre@...el.com>, <xiaoyao.li@...el.com>,
	<tony.lindgren@...ux.intel.com>, <binbin.wu@...ux.intel.com>,
	<isaku.yamahata@...el.com>, <linux-kernel@...r.kernel.org>,
	<yan.y.zhao@...el.com>, <chao.gao@...el.com>
Subject: Re: [PATCH V2 1/1] KVM: TDX: Add sub-ioctl KVM_TDX_TERMINATE_VM

On 19/04/25 04:08, Sean Christopherson wrote:
> On Fri, Apr 18, 2025, Vishal Annapurve wrote:
>> On Thu, Apr 17, 2025 at 6:20 AM Adrian Hunter <adrian.hunter@...el.com> wrote:
>>>
>>> ...
>>> +static int tdx_terminate_vm(struct kvm *kvm)
>>> +{
>>> +       int r = 0;
>>> +
>>> +       guard(mutex)(&kvm->lock);
>>> +       cpus_read_lock();
>>> +
>>> +       if (!kvm_trylock_all_vcpus(kvm)) {
>>
>> Does this need to be a trylock variant? Is userspace expected to keep
>> retrying this operation indefinitely?

No issue was seen in testing with a QEMU hack with no retrying.
Presumably if user space is not doing anything with the TDX VM at
the same time, then there should not be contention.

KVM_TDX_TERMINATE_VM is optional so it is not necessary to wait
indefinitely.

> Userspace is expected to not be stupid, i.e. not be doing things with vCPUs when
> terminating the VM.  This is already rather unpleasant, I'd rather not have to
> think hard about what could go wrong if KVM has to wait on all vCPU mutexes.