linux-kernel - Re: [PATCH 13/25] KVM: TDX: create/destroy VM structure

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Message-ID: <ZsWFiSAwKP8BfOUK@tlindgre-MOBL1>
Date: Wed, 21 Aug 2024 09:13:29 +0300
From: Tony Lindgren <tony.lindgren@...ux.intel.com>
To: Yuan Yao <yuan.yao@...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>,
	Sean Christopherson <sean.j.christopherson@...el.com>,
	Yan Zhao <yan.y.zhao@...el.com>
Subject: Re: [PATCH 13/25] KVM: TDX: create/destroy VM structure

On Wed, Aug 14, 2024 at 11:08:49AM +0800, Yuan Yao wrote:
> On Mon, Aug 12, 2024 at 03:48:08PM -0700, Rick Edgecombe wrote:
> > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > +static int __tdx_td_init(struct kvm *kvm)
> > +{
...
> > +	/*
> > +	 * TDH.MNG.CREATE tries to grab the global TDX module and fails
> > +	 * with TDX_OPERAND_BUSY when it fails to grab.  Take the global
> > +	 * lock to prevent it from failure.
> > +	 */
> > +	mutex_lock(&tdx_lock);
> > +	kvm_tdx->tdr_pa = tdr_pa;
> > +	err = tdh_mng_create(kvm_tdx, kvm_tdx->hkid);
> > +	mutex_unlock(&tdx_lock);
> > +
> > +	if (err == TDX_RND_NO_ENTROPY) {
> > +		kvm_tdx->tdr_pa = 0;
> 
> code path after 'free_packages' set it to 0, so this can be removed.
> 
> > +		ret = -EAGAIN;
> > +		goto free_packages;
> > +	}
> > +
> > +	if (WARN_ON_ONCE(err)) {
> > +		kvm_tdx->tdr_pa = 0;
> 
> Ditto.

Yes those seem unnecessary.

> > +	kvm_tdx->tdcs_pa = tdcs_pa;
> > +	for (i = 0; i < tdx_sysinfo_nr_tdcs_pages(); i++) {
> > +		err = tdh_mng_addcx(kvm_tdx, 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);
> > +			ret = -EIO;
> > +			goto teardown;
> 
> This and above 'goto teardown' under same for() free the
> partially added TDCX pages w/o take ownership back, may
> 'goto teardown_reclaim' (or any better name) below can
> handle this, see next comment for this patch.
...
> > +teardown:
> > +	for (; i < tdx_sysinfo_nr_tdcs_pages(); i++) {
> > +		if (tdcs_pa[i]) {
> > +			free_page((unsigned long)__va(tdcs_pa[i]));
> > +			tdcs_pa[i] = 0;
> > +		}
> > +	}
> > +	if (!kvm_tdx->tdcs_pa)
> > +		kfree(tdcs_pa);
> 
> Add 'teardown_reclaim:' Here, pair with my last comment.

Makes sense, I'll do patch.

Regards,

Tony