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Message-ID: <55eb8f3649590289a0f2b1ebe7583b6da3ff70ee.camel@kernel.org>
Subject: Re: [PATCH] x86/sgx: Free backing memory after faulting the enclave
 page
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     Dave Hansen <dave.hansen@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
        Jethro Beekman <jethro@fortanix.com>,
        Sean Christopherson <seanjc@google.com>
Cc:     reinette.chatre@intel.com, tony.luck@intel.com,
        nathaniel@profian.com, stable@vger.kernel.org,
        Borislav Petkov <bp@suse.de>, linux-sgx@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Thu, 04 Nov 2021 17:25:03 +0200
In-Reply-To: <d2191571-30a5-c2aa-e8ed-0a380e9daeac@intel.com>
References: <20211103232238.110557-1-jarkko@kernel.org>
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On Thu, 2021-11-04 at 08:13 -0700, Dave Hansen wrote:
> On 11/4/21 8:04 AM, Jarkko Sakkinen wrote:
> > > Do we also need to deal with truncating the PCMD?=C2=A0 (For those wa=
tching
> > > along at home, there are two things SGX swaps to RAM: the actual page
> > > data and also some metadata that ensures page integrity and helps
> > > prevent things like rolling back to old versions of swapped pages)
> > Yes.
> >=20
> > This can be achieved by iterating through all of the enclave pages,
> > which share the same shmem page for storing their PCMD's, as the one
> > being faulted back. If none of those pages is swapped, the PCMD page ca=
n
> > safely truncated.
>=20
> I was thinking we could just read the page.=C2=A0 If it's all 0's, trunca=
te it.

Hmm... did ELDU zero PCMD as a side-effect?

It should be fairly effecient just to check the pages by using
encl->page_tree.

/Jarkko