linux-kernel - Re: [PATCH] x86/sgx: Fix deadloop in __sgx_alloc_epc

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Message-ID: <ZtFjPwNWS_hfs4px@ziqianlu-kbl>
Date: Fri, 30 Aug 2024 14:14:23 +0800
From: Aaron Lu <aaron.lu@...el.com>
To: Jarkko Sakkinen <jarkko@...nel.org>
CC: Dave Hansen <dave.hansen@...ux.intel.com>, <x86@...nel.org>,
	<linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Zhimin Luo
	<zhimin.luo@...el.com>
Subject: Re: [PATCH] x86/sgx: Fix deadloop in __sgx_alloc_epc_page()

On Thu, Aug 29, 2024 at 07:44:13PM +0300, Jarkko Sakkinen wrote:
> On Thu Aug 29, 2024 at 5:38 AM EEST, Aaron Lu wrote:
> > When current node doesn't have a EPC section configured by firmware and
> > all other EPC sections memory are used up, CPU can stuck inside the
> > while loop in __sgx_alloc_epc_page() forever and soft lockup will happen.
> > Note how nid_of_current will never equal to nid in that while loop because
>                                                      ~~~~
> 
> Oh *that* while loop ;-) Please be more specific.

What about:
Note how nid_of_current will never be equal to nid in the while loop that
searches an available EPC page from remote nodes because nid_of_current is
not set in sgx_numa_mask.

> > nid_of_current is not set in sgx_numa_mask.
> >
> > Also worth mentioning is that it's perfectly fine for firmware to not
> > seup an EPC section on a node. Setting an EPC section on each node can
> > be good for performance but that's not a requirement functionality wise.
> 
> This lacks any description of what is done to __sgx_alloc_epc_page().

Will add what Dave suggested on how the problem is fixed to the changelog.

> >
> > Fixes: 901ddbb9ecf5 ("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()")
> > Reported-by: Zhimin Luo <zhimin.luo@...el.com>
> > Tested-by: Zhimin Luo <zhimin.luo@...el.com>
> > Signed-off-by: Aaron Lu <aaron.lu@...el.com>

Thanks,
Aaron