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

Re: [PATCH v2 5/7] xen/arm: Use sanitize values for p2m

  • To: Julien Grall <julien@xxxxxxx>
  • From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
  • Date: Mon, 23 Aug 2021 13:37:16 +0000
  • Accept-language: en-GB, en-US
  • Arc-authentication-results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=arm.com; dmarc=pass action=none header.from=arm.com; dkim=pass header.d=arm.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=yDAY3uCWOIIsn7O7NSAGWtXEUQOoxP5EGUNrLlpqKEw=; b=HvQe0u1TSrUUOHIcOS/obagbq7YKH7k1cc+Cm6LtqOx1KOpkjCF1h+1OtlEEupvL9hSdo8EUBH2iH8Lqs6iQ3PxC/2OtdXL7YPT4GyuJHqMzQuBCcEhCIzuZBiBK4WYsU0FSNXf5Kq9rj37GxMQ/UzpncU7r5ald6LtvrMkH3UJ28xn1fOwq4DJv43PfUIAnUVxy1Yth91NYBVGy2tTkJj9sjucx8oSj2IWV0J1nb2/sg01Dn7EpLeDhg+KYgbHO3nHXHI2vJDEka5AbrS1gTrH3y9bxfCFx1kJA/FGGXxZzc6GgJ7SW1lMD/qgO/m07tVhqu0FOX9vebcmLS6A8Cw==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=CAq1Y/pQaPzM1YrgP3g/lmQVCSjD5ysHB42uNJBVVqNDToQXpyTSTo3lR6V2kA44kzTrVugyDaSmNOaHXIbsUVYphvpis6oc8NtOBUAYVOONr8sh3tz1aqnOERuW4sJsz0hprWxp6agkMmpRPYSAxScCsoqcrXkf87J8OywLCzwui0foeSGaGpejoa48qc/RG0dz43B9osdLGhDLeenGXJUixmLqaF2N4y/BsfqRQTihzvQ1d8pKpmlx1IcpYE+gqpbxNXql1+NRki5I/wldh50INCaiy2TlTS0xOQeL4VuF1A+k62/45laZSZwnxSTV9ABwgdABTNqLGBgrRaf4GA==
  • Authentication-results-original: xen.org; dkim=none (message not signed) header.d=none;xen.org; dmarc=none action=none header.from=arm.com;
  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
  • Delivery-date: Mon, 23 Aug 2021 13:37:37 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Nodisclaimer: true
  • Original-authentication-results: xen.org; dkim=none (message not signed) header.d=none;xen.org; dmarc=none action=none header.from=arm.com;
  • Thread-topic: [PATCH v2 5/7] xen/arm: Use sanitize values for p2m


> On 23 Aug 2021, at 14:22, Julien Grall <julien@xxxxxxx> wrote:
> On 23/08/2021 13:39, Bertrand Marquis wrote:
>> Hi Julien,
> Hi Bertrand,
>>> On 23 Aug 2021, at 12:47, Julien Grall <julien@xxxxxxx> wrote:
>>> Hi Bertrand,
>>> On 23/08/2021 11:32, Bertrand Marquis wrote:
>>>> Replace the code in p2m trying to find a sane value for the VMID size
>>>> supported and the PAR to use. We are now using the boot cpuinfo as the
>>>> values there are sanitized during boot and the value for those
>>>> parameters is now the safest possible value on the system.
>>>> On arm32, the system will panic if there are different types of core so
>>>> those checks were not needed anyway.
>>> So the assumption is that if you have the same MIDR, then you must have the 
>>> same features. I understand this is what Xen assumes today but I never 
>>> viewed that check as the truth. It is more to limit the damage on most 
>>> platform.
>> This was the assumption before, I did not change anything but just explained 
>> in the commit message why this was not possible to come to this code.
> Yes. This is not a new, however I thought I would mention it because I want 
> to avoid continuing to use wrong assumptions.
> However, this code is arm64 only as it is #ifdef right? (Sorry I should have 
> looked at the code the first time) So ...
>>> So can you confirm whether this is something that Arm guarantees?
>> For a specific MIDR from Arm (ie a Cortex) the PAR is fixed and VMID size to.
>> But for an other Arm architecture processor I cannot say.
>>> That said, I am not against removing the code. But I would like the comment 
>>> to be amended if this is not a correct assumption.
>> Would the following be acceptable:
>> On arm32, Xen is not booting on systems having different MIDR amongst cores 
>> and it is assumed that cores with the same MIDR will have the same PAR and 
>> VMID size.
> ... I would just drop any mention of arm32 here.



> Cheers,
> -- 
> Julien Grall



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