linux-kernel - Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure

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Date: Thu, 4 Apr 2024 11:26:19 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, Paolo Bonzini
	<pbonzini@...hat.com>, "Aktas, Erdem" <erdemaktas@...gle.com>, "Sean
 Christopherson" <seanjc@...gle.com>, Sagi Shahar <sagis@...gle.com>, "Chen,
 Bo2" <chen.bo@...el.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Zhang, Tina"
	<tina.zhang@...el.com>, Sean Christopherson
	<sean.j.christopherson@...el.com>, "isaku.yamahata@...ux.intel.com"
	<isaku.yamahata@...ux.intel.com>
Subject: Re: [PATCH v19 038/130] KVM: TDX: create/destroy VM structure



On 4/04/2024 6:24 am, Yamahata, Isaku wrote:
> On Thu, Mar 28, 2024 at 12:33:35PM +1300,
> "Huang, Kai" <kai.huang@...el.com> wrote:
> 
>>> +	kvm_tdx->tdr_pa = tdr_pa;
>>> +
>>> +	for_each_online_cpu(i) {
>>> +		int pkg = topology_physical_package_id(i);
>>> +
>>> +		if (cpumask_test_and_set_cpu(pkg, packages))
>>> +			continue;
>>> +
>>> +		/*
>>> +		 * Program the memory controller in the package with an
>>> +		 * encryption key associated to a TDX private host key id
>>> +		 * assigned to this TDR.  Concurrent operations on same memory
>>> +		 * controller results in TDX_OPERAND_BUSY.  Avoid this race by
>>> +		 * mutex.
>>> +		 */
>>
>> IIUC the race can only happen when you are creating multiple TDX guests
>> simulatenously?  Please clarify this in the comment.
>>
>> And I even don't think you need all these TDX module details:
>>
>> 		/*
>> 		 * Concurrent run of TDH.MNG.KEY.CONFIG on the same
>> 		 * package resluts in TDX_OPERAND_BUSY.  When creating
>> 		 * multiple TDX guests simultaneously this can run
>> 		 * concurrently.  Take the per-package lock to
>> 		 * serialize.
>> 		 */
> 
> As pointed by Chao, those mutex will be dropped.
> https://lore.kernel.org/kvm/ZfpwIespKy8qxWWE@chao-email/
> Also we would simplify cpu masks to track which package is online/offline,
> which cpu to use for each package somehow.

Please see my reply there.  I might be missing something, though.

> 
> 
>>> +		mutex_lock(&tdx_mng_key_config_lock[pkg]);
>>> +		ret = smp_call_on_cpu(i, tdx_do_tdh_mng_key_config,
>>> +				      &kvm_tdx->tdr_pa, true);
>>> +		mutex_unlock(&tdx_mng_key_config_lock[pkg]);
>>> +		if (ret)
>>> +			break;
>>> +	}
>>> +	cpus_read_unlock();
>>> +	free_cpumask_var(packages);
>>> +	if (ret) {
>>> +		i = 0;
>>> +		goto teardown;
>>> +	}
>>> +
>>> +	kvm_tdx->tdcs_pa = tdcs_pa;
>>> +	for (i = 0; i < tdx_info->nr_tdcs_pages; i++) {
>>> +		err = tdh_mng_addcx(kvm_tdx->tdr_pa, tdcs_pa[i]);
>>> +		if (err == TDX_RND_NO_ENTROPY) {
>>> +			/* Here it's hard to allow userspace to retry. */
>>> +			ret = -EBUSY;
>>> +			goto teardown;
>>> +		}
>>> +		if (WARN_ON_ONCE(err)) {
>>> +			pr_tdx_error(TDH_MNG_ADDCX, err, NULL);
>>> +			ret = -EIO;
>>> +			goto teardown;
>>> +		}
>>> +	}
>>> +
>>> +	/*
>>> +	 * Note, TDH_MNG_INIT cannot be invoked here.  TDH_MNG_INIT requires a dedicated
>>> +	 * ioctl() to define the configure CPUID values for the TD.
>>> +	 */
>>
>> Then, how about renaming this function to __tdx_td_create()?
> 
> So do we want to rename also ioctl name for consistency?
> i.e. KVM_TDX_INIT_VM => KVM_TDX_CREATE_VM.

Hmm.. but this __tdx_td_create() (the __tdx_td_init() in this patch) is 
called via kvm_x86_ops->vm_init(), but not IOCTL()?

If I read correctly, only TDH.MNG.INIT is called via IOCTL(), in that 
sense it makes more sense to name the IOCTL() as KVM_TDX_INIT_VM.

> 
> I don't have strong opinion those names. Maybe
> KVM_TDX_{INIT, CREATE, or CONFIG}_VM?
> And we can rename the function name to match it.
>