[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH 3/5] x86/PV: _PAGE_RW changes may take fast path of mod_l[234]_entry()


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Mon, 11 Jan 2021 15:26:03 +0100
  • Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none
  • Arc-message-signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=o/x2FTPAzgwYY4bB9bWOK8CrM9sC0tJrv9hcZuZ5xn4=; b=ZHetKfQpy7Y2J8TunkfY6ArdLNMjTWnB6CdO3isZrnOH2up+3DNAQIcKI/C/nHTTcoHxkbQRRMttUL0TQH2UxQ1sLs4F9ib3VQqqLVPk07fegZgewKgpia46XKOpfd77He55yHKx+YzJki+mDlJPak+InmFMWFLrVngr2+mkcUStNjHLr+mKQP/uELW1EciU8FYIPfLRnv4x2s6KssacHc8jk7BpyyAHuSrD+OiJwNzaQ5JWzcgmIzjbdhXhTPLWoz+4EfyphXpEymwBc+ogS+yrjUBBfMqV4R8cX+wTq2MtbZf4BlOT474YHAmj4BY5BVa3xAXB6VDKIT4eCN1VAA==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=UdUxgzgysZK0Yb+kJuOiutDWxxIiTIXjU2Wbp1WR31nd2EtjOzC+6+ofOdNCcsQ1fxQOS1gxwZ42NPz2g8Rao/8+qk8kke25UBGwDuvDv6gkZp8u9mCIqYC8pcC1PawwBY+qT4DBLl8V38jAsbgAfx+Nvp+DJ7FcoYgbd/+IDvERn4IJzGdWA52/NtGZwiIZGvKUoH+4jtP2abvw1qJw8TPkEcIht1JkVcy0nxDEwtXmYlvBbqIaW4bdn2/1TDYgF+K3VWe8qRUZHb1rgI724mWDIt2gvnV72eAQgwjTyJQfIJrk9U8vg3QL2ZVS0jjxBdKhWNtGYhlQjxH4/4cPTw==
  • Authentication-results: esa2.hc3370-68.iphmx.com; dkim=pass (signature verified) header.i=@citrix.onmicrosoft.com
  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>
  • Delivery-date: Mon, 11 Jan 2021 14:26:17 +0000
  • Ironport-sdr: 6ErkfSsr1KapbrBLz2vWnuzrn0tCGWLCWcXjnKeGA+hMlqTeEETVDA0MWDhWvPE22qHnkPsoUa mCWdXytOIJlUeABaOGB4lZ6UDGdk7fr3dTAepdjvainaL2nzmBJb/ZNM3CeaXdWfriWkhZO9jz cOAAIAAMLAIkEbIoOqV00pEeJnDYUhhSDDdvnhDtRcSlt2p0kA+0/kx+XwuiGzLrEoQuV8Cb4e /uqtbX4LgaWukPWvII2LY+P1OPQwhXTKJB4UGh66k2YpfPiH7IIoWG8tnY52Mx04n3sceDejo4 Z0M=
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On Mon, Jan 11, 2021 at 02:31:10PM +0100, Jan Beulich wrote:
> On 11.01.2021 12:08, Roger Pau Monné wrote:
> > On Tue, Nov 03, 2020 at 11:57:10AM +0100, Jan Beulich wrote:
> >> The only time _PAGE_RW matters when validating an L2 or higher entry is
> >> when a linear page table is tried to be installed. Therefore when we
> >> disallow such at build time, we can allow _PAGE_RW changes to take the
> >> fast paths there.
> > 
> > I think it would be helpful to note why PDEs with linear page tables
> > aren't allowed to have the RW bit set, likely here and in the comment
> > below.
> 
> I've changed the description to
> 
> "The only time _PAGE_RW matters when validating an L2 or higher entry is
>  when a linear page table is tried to be installed (see the comment ahead
>  of define_get_linear_pagetable()). Therefore when we disallow such at
>  build time, we can allow _PAGE_RW changes to take the fast paths there."
> 
> Considering there already is a code comment explaining this, I'm
> less convinced of also editing the comment. An option might be to
> move up the #define-s next to define_get_linear_pagetable(), but
> imo this should then involve moving FASTPATH_FLAG_WHITELIST as
> well.

Referencing the comment in define_get_linear_pagetable in the commit
message seems fine to me:

Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.



 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.