Re: [RFC PATCH v0 0/6] x86/AMD: Userspace address tagging

[Dave Hansen]

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@xxxxxxxxxxxxxxx/

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.