linux-kernel - Re: [PATCH v3 17/28] x86/sgx: fix a NULL pointer

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Message-Id: <CU4IS5XRH3PK.M9DAVXJ7PSSE@seitikki>
Date:   Mon, 17 Jul 2023 14:33:46 +0000
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Haitao Huang" <haitao.huang@...ux.intel.com>,
        <dave.hansen@...ux.intel.com>, <tj@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-sgx@...r.kernel.org>,
        <cgroups@...r.kernel.org>, "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>
Cc:     <kai.huang@...el.com>, <reinette.chatre@...el.com>,
        <zhiquan1.li@...el.com>, <kristen@...ux.intel.com>,
        <seanjc@...gle.com>
Subject: Re: [PATCH v3 17/28] x86/sgx: fix a NULL pointer

On Mon Jul 17, 2023 at 1:14 PM UTC, Haitao Huang wrote:
> On Mon, 17 Jul 2023 07:49:27 -0500, Jarkko Sakkinen <jarkko@...nel.org>  
> wrote:
>
> > On Mon Jul 17, 2023 at 12:48 PM UTC, Jarkko Sakkinen wrote:
> >> On Wed Jul 12, 2023 at 11:01 PM UTC, Haitao Huang wrote:
> >> > Under heavy load, the SGX EPC reclaimers (ksgxd or future EPC cgroup
> >> > worker) may reclaim SECS EPC page for an enclave and set
> >> > encl->secs.epc_page to NULL. But the SECS EPC page is required for  
> >> EAUG
> >> > in #PF handler and is used without checking for NULL and reloading.
> >> >
> >> > Fix this by checking if SECS is loaded before EAUG and load it if it  
> >> was
> >> > reclaimed.
> >> >
> >> > Signed-off-by: Haitao Huang <haitao.huang@...ux.intel.com>
> >>
> >> A bug fix should be 1/*.
> >
> > And a fixes tag.
> >
> > Or is there a bug that is momentized by the earlier patches? This patch
> > feels confusing to say the least.
> >
>
> It happens in heavy reclaiming cases, just extremely rare when EPC  
> accounting is not partitioned into cgroups. Will add fix tag with the  
> related EDMM patch. And move this as the first patch.

I understand, it is just a good practice to follow, i.e. have prelude
and then the "real" changes :-)

BR, Jarkko