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Message-ID: <e4e8fbe757860cd24e2f66b25be60d76663935d8.camel@kernel.org>
Subject: Re: [PATCH] x86/sgx: Silence softlockup detection when releasing
 large enclaves
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Reinette Chatre <reinette.chatre@intel.com>,
        dave.hansen@linux.intel.com, tglx@linutronix.de, bp@alien8.de,
        luto@kernel.org, mingo@redhat.com, linux-sgx@vger.kernel.org,
        x86@kernel.org
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Date:   Thu, 20 Jan 2022 15:01:29 +0200
In-Reply-To: <1aa037705e5aa209d8b7a075873c6b4190327436.1642530802.git.reinette.chatre@intel.com>
References: <1aa037705e5aa209d8b7a075873c6b4190327436.1642530802.git.reinette.chatre@intel.com>
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On Tue, 2022-01-18 at 11:14 -0800, Reinette Chatre wrote:
> Vijay reported that the "unclobbered_vdso_oversubscribed" selftest
> triggers the softlockup detector.
>=20
> Actual SGX systems have 128GB of enclave memory or more.=C2=A0 The
> "unclobbered_vdso_oversubscribed" selftest creates one enclave which
> consumes all of the enclave memory on the system. Tearing down such a
> large enclave takes around a minute, most of it in the loop where
> the EREMOVE instruction is applied to each individual 4k enclave
> page.
>=20
> Spending one minute in a loop triggers the softlockup detector.
>=20
> Add a cond_resched() to give other tasks a chance to run and placate
> the softlockup detector.
>=20
> Cc: stable@vger.kernel.org
> Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
> Reported-by: Vijay Dhanraj <vijay.dhanraj@intel.com>
> Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> Softlockup message:
> watchdog: BUG: soft lockup - CPU#7 stuck for 22s! [test_sgx:11502]
> Kernel panic - not syncing: softlockup: hung tasks
> <snip>
> sgx_encl_release+0x86/0x1c0
> sgx_release+0x11c/0x130
> __fput+0xb0/0x280
> ____fput+0xe/0x10
> task_work_run+0x6c/0xc0
> exit_to_user_mode_prepare+0x1eb/0x1f0
> syscall_exit_to_user_mode+0x1d/0x50
> do_syscall_64+0x46/0xb0
> entry_SYSCALL_64_after_hwframe+0x44/0xae
>=20
> =C2=A0arch/x86/kernel/cpu/sgx/encl.c | 1 +
> =C2=A01 file changed, 1 insertion(+)
>=20
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c
> b/arch/x86/kernel/cpu/sgx/encl.c
> index 001808e3901c..ab2b79327a8a 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -410,6 +410,7 @@ void sgx_encl_release(struct kref *ref)
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0}
> =C2=A0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0kfree(entry);
> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0cond_resched();
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0}
> =C2=A0
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0xa_destroy(&encl->page_ar=
ray);

I'd add a comment, e.g.

/* Invoke scheduler to prevent soft lockups. */

Other than that makes sense.

BR, Jarkko