linux-kernel - Re: [PATCH v4 1/3] x86/sgx: Use sgx_free_epc_page() in sgx_reclaim

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Message-ID: <YE+wMvw4YuDKu1xx@kernel.org>
Date:   Mon, 15 Mar 2021 21:06:26 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     linux-sgx@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/3] x86/sgx: Use sgx_free_epc_page() in
 sgx_reclaim_pages()

On Mon, Mar 15, 2021 at 08:32:13AM -0700, Dave Hansen wrote:
> On 3/13/21 8:01 AM, Jarkko Sakkinen wrote:
> > Replace the ad-hoc code with a sgx_free_epc_page(), in order to make sure
> > that all the relevant checks and book keeping is done, while freeing a
> > borrowed EPC page, and remove redundant code. EREMOVE inside
> > sgx_free_epc_page() does not change the semantics, as EREMOVE to an
> > uninitialize pages is a nop.
> 
>   ^ uninitialized
> 
> I know this is a short patch, but this changelog still falls a bit short
> for me.
> 
> Why is this patch a part of _this_ series?  What *problem* does it
> solve, related to this series?

I'm thinking of merging sgx_epc_section and sgx_numa_node. That's why I
kept it as part of the series. 

Also, in any case it's better to clean up duplicate functionality. The
code is essentially open coded implementation of sgx_free_epc_page()
without EREMOVE.

> It would also be nice to remind me why the EREMOVE is redundant.  Why
> didn't we need one before?  What put the page in the uninitialized
> state?  Is EREMOVE guaranteed to do nothing?  How expensive is it?

EREMOVE gets removed by KVM series from sgx_free_epc_page() anyway.

Maybe should re-send this patch, or series, after KVM series is merged.
Then there is no explaining with EREMOVE, as sgx_free_epc_page() won't
contain it.

/Jarkko