linux-kernel - Re: [PATCH] x86/mm: Don't try to change poison pages to uncacheable in a guest

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Message-ID: <CAPcyv4iLMzGJUgjG9kxuuH65mYbqJ0+oHd4DbD1Kc6p9J14F0g@mail.gmail.com>
Date:   Mon, 18 May 2020 12:20:59 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, Jue Wang <juew@...gle.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/mm: Don't try to change poison pages to uncacheable
 in a guest

On Mon, May 18, 2020 at 11:26 AM Luck, Tony <tony.luck@...el.com> wrote:
[..]
> N.B. Linux wants to switch the page to uncacheable so that in the
> persistant memory case the filesytem code can continue to access
> the other "blocks" in the page, rather than lose all of them. That's
> futile in the case where the VMM took the whole 4K away. Maybe Dan
> needs to think about the guest case too.

I think increasing the blast-radius to 4K is the best we can do
without a paravirt mechanism to coordinate errors. There's also the
existing problem that set_mce_nospec() fails on pmem due to the
memtype lookup.