Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <81b6f618-05bc-f7d0-5461-4c3f0ca42d3f@intel.com>
Date:   Thu, 10 Mar 2022 07:16:27 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Content-Language: en-US
To:     Bharata B Rao <bharata@amd.com>, linux-kernel@vger.kernel.org
Cc:     linux-mm@kvack.org, x86@kernel.org,
        kirill.shutemov@linux.intel.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        catalin.marinas@arm.com, will@kernel.org, shuah@kernel.org,
        oleg@redhat.com, ananth.narayan@amd.com
References: <20220310111545.10852-1-bharata@amd.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [RFC PATCH v0 0/6] x86/AMD: Userspace address tagging
In-Reply-To: <20220310111545.10852-1-bharata@amd.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 3/10/22 03:15, Bharata B Rao wrote:>
> This patchset builds on that prctl() extension and adds support
> for AMD UAI. AMD implementation is kept separate as equivalent
> Intel LAM implementation is likely to be different due to different
> bit positions and tag width.

Please don't keep the implementations separate.

We'll have one x86 implementation of address bit masking.  Both the
Intel and AMD implementations will feed into a shared implementation.
Something _like_ the cc_set_mask() interface where both implementations
do their detection and then call into common code to say how many bits
are being ignored.

A good litmus test for this is how many vendor-specific checks there are
in common code.  If there are a lot of them, it's not a good sign for
the design.

I'd also highly suggest going over Kirill's patch set in detail.  There
are things like this:

> https://lore.kernel.org/linux-mm/20210205151631.43511-10-kirill.shutemov@linux.intel.com/

which seem pretty sane to me but which are (I think) missing in this set.

I don't know if we can get there but, in an ideal world, this would be
series with, say 7 patches.  Patches 1-5 are generic enabling.  Patch 6
is tiny and does detection and enabling for UAI.  Patch 7 does the same
for LAM.  All the patches in the series are acked from LAM and UAI folks.