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From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
	Wei Liu <wl@xen.org>, Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v3] x86/PV: remove unnecessary toggle_guest_pt() overhead
Date: Mon, 18 May 2020 18:52:13 +0200	[thread overview]
Message-ID: <20200518165213.GX54375@Air-de-Roger> (raw)
In-Reply-To: <24d8b606-f74b-9367-d67e-e952838c7048@suse.com>

On Tue, May 05, 2020 at 08:16:03AM +0200, Jan Beulich wrote:
> While the mere updating of ->pv_cr3 and ->root_pgt_changed aren't overly
> expensive (but still needed only for the toggle_guest_mode() path), the
> effect of the latter on the exit-to-guest path is not insignificant.
> Move the logic into toggle_guest_mode(), on the basis that
> toggle_guest_pt() will always be invoked in pairs, yet we can't safely
> undo the setting of root_pgt_changed during the second of these
> invocations.

I'm not sure if it would be worth to add a comment to note the
intended usage of toggle_guest_pt is to fetch data from the kernel
page tables when running in user mode. The one about using it in pairs
is certainly fine.

> While at it, add a comment ahead of toggle_guest_pt() to clarify its
> intended usage.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks, Roger.


  reply	other threads:[~2020-05-18 16:52 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05  6:16 [PATCH v3] x86/PV: remove unnecessary toggle_guest_pt() overhead Jan Beulich
2020-05-18 16:52 ` Roger Pau Monné [this message]
2020-05-21 16:46 ` Andrew Cooper
2020-05-22 10:07   ` Jan Beulich
2020-05-29 16:24     ` Andrew Cooper

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