linux-kernel - Re: [RFC PATCH v2 1/1] x86/sgx: Explicitly give up the CPU in EDMM's ioctl() to avoid softlockup

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Message-ID: <30415ed3-a05a-454d-9077-c8674617f291@intel.com>
Date: Fri, 26 Apr 2024 10:06:56 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Bojun Zhu <zhubojun.zbj@...group.com>, linux-kernel@...r.kernel.org,
 linux-sgx@...r.kernel.org, jarkko@...nel.org, dave.hansen@...ux.intel.com
Cc: reinette.chatre@...el.com, 刘双(轩屹)
 <ls123674@...group.com>
Subject: Re: [RFC PATCH v2 1/1] x86/sgx: Explicitly give up the CPU in EDMM's
 ioctl() to avoid softlockup

On 4/26/24 07:18, Bojun Zhu wrote:
>  	for (c = 0 ; c < modp->length; c += PAGE_SIZE) {
> +		if (sgx_check_signal_and_resched()) {
> +			if (!c)
> +				ret = -ERESTARTSYS;
> +
> +			goto out;
> +		}

This construct is rather fugly.  Let's not perpetuate it, please.  Why
not do:

	int ret = -ERESTARTSYS;

	...
	for (c = 0 ; c < modp->length; c += PAGE_SIZE) {
		if (sgx_check_signal_and_resched())
			goto out;

Then, voila, when c==0 on the first run through the loop, you'll get a
ret=-ERESTARTSYS.

But honestly, it seems kinda silly to annotate all these loops with
explicit cond_resched()s.  I'd much rather do this once and, for
instance, just wrap the enclave locks:

-	  mutex_lock(&encl->lock);
+	  sgx_lock_enclave(encl);

and then have the lock function do the rescheds.  I assume that
mutex_lock() isn't doing this generically for performance reasons.  But
we don't care in SGX land and can just resched to our heart's content.