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

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Message-Id: <D3WS02D8SZMG.62T9IWX6WZI4@kernel.org>
Date: Tue, 03 Sep 2024 19:05:40 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Aaron Lu" <aaron.lu@...el.com>
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 Fri Aug 30, 2024 at 9:14 AM EEST, Aaron Lu wrote:
> 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.

That would work I think!

>
> > > 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.

Great. I think the code change is correct reflecting these additions.
I'll look the next version as a whole but with high probability I can
ack that as long as the commit message has these updates.

>
> > >
> > > 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

BR, Jarkko