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

Re: meaning and use of IOMMU_FLUSHF_added

  • To: Paul Durrant <paul@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 18 Aug 2021 14:09:41 +0200
  • Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=suse.com; dmarc=pass action=none header.from=suse.com; dkim=pass header.d=suse.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=5KPWinKbWR14fGcKfhcZWMUqQPi3/q/25h9/w5coZ1k=; b=N3WFPN4rh2NP+VJsADnKsMHEq30G9OK4GRAkbA6TkF4ENnAhPnxjah1+/mvXv5W+Y1Ej6Y6QiVb1VpFtM1g/Lmy5jBGpM4+ggNOlzXbkiXRMv8jhejshCKT/1vn82Nacb2T8BIAyBIr4xe5R8oTeevcDr7EUV9yzRviD8Zs1vn10FgH5uqnH17XneQX7wmABWNzNWx5cs0pGIe9qz6/dDUc31VeKSdEFDNrfDzfaWbmyCT097ZQ5eDKybsHJI2Xamlw79u39lHdQMUAacp9Wa9cYyzjjyIwWK9XrLHSITQMGNsJXxT93FEpWGYtfTKqc+L+gPR/jvmfcQMQ9rrkpUg==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=kEDRI1DNb0yWNESuatfFVkyIgh4jsabzyhbWEBasQSH/AGKU/C1awQR1pXZ1vXzexhxGVDOLp3JEZofzCipZtLi5qpVM08HLmzYk2q25ItjwNmZ8SsS4/APDNXrOae5j3ryPtD0s1Sd7+rztQzy0Pha7Wm6OY5ZgTXlmAszHO094aBhX942wy0TtwkrY171O4PSxsamPjT6yt08Kz3Se96xA0lEFMIE8Okh3PPyg7EbWJM1YA6QTgt7O8beqCFBqnalb9PuPVfAaUhnwGWcdHiHf4Is1pn14MbkzJYml5B9yo0ymWNFJ2KuLzB8LWRYVJfLGqdoPFbhc6PhazhvkJA==
  • Authentication-results: lists.xenproject.org; dkim=none (message not signed) header.d=none;lists.xenproject.org; dmarc=none action=none header.from=suse.com;
  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Wed, 18 Aug 2021 12:09:54 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 18.08.2021 12:51, Jan Beulich wrote:
> Paul,
> back at the time I did already question your intended meaning of
> this flag. I notice that there's presently no consumer of it being
> set (apart from yielding non-zero flush_flags). I'm afraid this
> model makes accumulation of flush flags not work properly: With
> both flags set and more than a single page altered, it is
> impossible to tell apart whether two present PTEs were altered, or
> a non-present and a present one.
> VT-d's flushing needs to know the distinction; it may in fact be
> necessary to issue two flushes (or a single "heavier" one) when
> both non-present and present entries got transitioned to present
> in one go.

No two (or "heavier") flush looks to be needed upon further reading.
I did derive this from our setting of "did" to zero in that case,
but that looks to be wrong in the first place - it's correct only
for context cache entry flushes. I'll make a(nother) patch ...




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