From: Jan Beulich <jbeulich@suse.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org,
Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
Paul Durrant <paul@xen.org>
Subject: Re: [PATCH] Revert "x86/hvm: simplify 'mmio_direct' check in epte_get_entry_emt()"
Date: Tue, 8 Sep 2020 10:55:06 +0200 [thread overview]
Message-ID: <8a050491-4e02-63be-c622-6fab25c4c2e6@suse.com> (raw)
In-Reply-To: <20200907170916.61693-1-roger.pau@citrix.com>
On 07.09.2020 19:09, Roger Pau Monne wrote:
> This reverts commit 81fd0d3ca4b2cd309403c6e8da662c325dd35750.
>
> Original commit only takes into account the APIC access page being a
> 'special' page, but when running a PVH dom0 there are other pages that
> also fulfill the 'special' page check but shouldn't have it's cache
> type set to WB.
>
> For example the ACPI regions are identity mapped into the guest but
> are also Xen heap pages, and forcing those to WB cache type is wrong.
Why is this wrong? Xen heap pages are RAM ones. Quite the opposite,
_not_ forcing them to WB is going to cause cachability conflicts,
unless their direct mapping entries also got changed to UC (which I
think we want to avoid if at all possible). The cachability we
select here is the one to be used by the hardware, not the one
perceived by a domain (be it Dom0 or a DomU).
> I've discovered this while trying to boot a PVH dom0, which fail to
> boot with this commit applied.
And what exactly is the deeper reason of the failure?
Jan
prev parent reply other threads:[~2020-09-08 8:55 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-07 17:09 [PATCH] Revert "x86/hvm: simplify 'mmio_direct' check in epte_get_entry_emt()" Roger Pau Monne
2020-09-08 6:47 ` Paul Durrant
2020-09-08 7:45 ` Roger Pau Monné
2020-09-08 8:55 ` Jan Beulich [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=8a050491-4e02-63be-c622-6fab25c4c2e6@suse.com \
--to=jbeulich@suse.com \
--cc=andrew.cooper3@citrix.com \
--cc=paul@xen.org \
--cc=roger.pau@citrix.com \
--cc=wl@xen.org \
--cc=xen-devel@lists.xenproject.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.