linux-kernel - Re: [PATCH 09/25] KVM: TDX: Get system-wide info about TDX module on initialization

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Message-ID: <ZtVHhC24JKnwNCIC@tlindgre-MOBL1>
Date: Mon, 2 Sep 2024 08:05:08 +0300
From: Tony Lindgren <tony.lindgren@...ux.intel.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>
Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>, seanjc@...gle.com,
	pbonzini@...hat.com, kvm@...r.kernel.org, kai.huang@...el.com,
	isaku.yamahata@...il.com, xiaoyao.li@...el.com,
	linux-kernel@...r.kernel.org,
	Isaku Yamahata <isaku.yamahata@...el.com>,
	Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH 09/25] KVM: TDX: Get system-wide info about TDX module on
 initialization

On Mon, Sep 02, 2024 at 09:25:00AM +0800, Xu Yilun wrote:
> > > > +static int tdx_get_capabilities(struct kvm_tdx_cmd *cmd)
> > > > +{
> > > > +	const struct tdx_sysinfo_td_conf *td_conf = &tdx_sysinfo->td_conf;
> > > > +	struct kvm_tdx_capabilities __user *user_caps;
> > > > +	struct kvm_tdx_capabilities *caps = NULL;
> > > > +	int i, ret = 0;
> > > > +
> > > > +	/* flags is reserved for future use */
> > > > +	if (cmd->flags)
> > > > +		return -EINVAL;
> > > > +
> > > > +	caps = kmalloc(sizeof(*caps), GFP_KERNEL);
> > > > +	if (!caps)
> > > > +		return -ENOMEM;
> > > > +
> > > > +	user_caps = u64_to_user_ptr(cmd->data);
> > > > +	if (copy_from_user(caps, user_caps, sizeof(*caps))) {
> > > > +		ret = -EFAULT;
> > > > +		goto out;
> > > > +	}
> > > > +
> > > > +	if (caps->nr_cpuid_configs < td_conf->num_cpuid_config) {
> > > > +		ret = -E2BIG;
> > > 
> > > How about output the correct num_cpuid_config to userspace as a hint,
> > > to avoid user blindly retries.
> > 
> > Hmm do we want to add also positive numbers for errors for this function?
> 
> No. I think maybe update the user_caps->nr_cpuid_configs when returning
> -E2BIG. Similar to KVM_GET_MSR_INDEX_LIST.

OK thanks for clarifying, yes that sounds nice.

Regards,

Tony