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

Re: [PATCH v5 08/11] xen/arm: Enable the existing x86 virtual PCI support for ARM.

  • To: Julien Grall <julien@xxxxxxx>
  • From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
  • Date: Tue, 12 Oct 2021 16:12:16 +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-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=71MFZnlzbv/YzYcN5M7r8f/Ot4fDlYY3vNHI4mHN9As=; b=mDTC9qK1WYcL0NnwU8YV6HtY92zTvd79Iv+hb429tZHI+GaJGhbRN9Fb0xaTZlUYQHeovjpm+otcSqSZYhpBq0CfHXrBBA1sP1TyubFRMuLA/LlF209r36c6Jkt0O62LMX37eIhYVGvi4Ylw8YwOnV/wO+h+WXifJEbEjirk+O3o9rc5aTgC3PilWvKUHoCsi5p+jx10o8GhqFXTSVBvdYHIW/luPMgYqwNM94bnq5/KiHx/+7CBj8vLLvq1x/UGZgrudoPt+29k3F9dkkGyX/BDZK3hrODzNMXxEInec/Qc5urVkYUJxNXhst76nX2zvBbHU9n24C2ysh3PrqbqzQ==
  • Arc-seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=nEb3CAVt8tlrhoqZVn9HNLjQfaLfEiNsSpvucRwMhpajoNA8WoKvGOuH+h1N/tz/FbzDv/FULjIVYHOUUjJkgy3b22T4BpR6B7SnU4JmC1+5y3fB1v9mc6+01rsXDpGZBuvFleloLlGptFTJtfuSRU2oocUO7vCV8aQlIbJ1Jfe4grnLctWh5T4ro0R5CA+t3O79Fh/gB+SzV8IVt7Vgv9OTUeCJhVfwD04l5Ww7g6DeVRZ9LSn5uZUj5XzrTzTCIYvEwvInFWv+tgy3yWR5BcwMp//NI2bYfbIaljGw83/4+sWGiqiAAgoP6FYwMNHe5ebyNsYaRHnghiudDF7pVw==
  • Authentication-results-original: xen.org; dkim=none (message not signed) header.d=none;xen.org; dmarc=none action=none header.from=arm.com;
  • Cc: Jan Beulich <jbeulich@xxxxxxxx>, Rahul Singh <Rahul.Singh@xxxxxxx>, Andre Przywara <Andre.Przywara@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 12 Oct 2021 16:12:46 +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-index: AQHXutl3YqS5dHXsYk6KpdKt4d14RavHjPqAgAY38oCAAbo3AIAAEwAA
  • Thread-topic: [PATCH v5 08/11] xen/arm: Enable the existing x86 virtual PCI support for ARM.

Hi Julien,

> On 12 Oct 2021, at 16:04, Julien Grall <julien@xxxxxxx> wrote:
> On 11/10/2021 13:41, Bertrand Marquis wrote:
>> Hi Jan,
> Hi Bertrand,
>> As Rahul is on leave, I will answer you and make the changes needed.
>>> On 7 Oct 2021, at 14:43, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>> Independent of this - is bare metal Arm enforcing this same
>>> alignment restriction (unconditionally)? Iirc on x86 we felt we'd
>>> better synthesize misaligned accesses.
>> Unaligned IO access could be synthesise also on arm to but I would
>> rather not make such a change now without testing it (and there is
>> also a question of it making sense).
> Yes it makes sense. I actually have an item in my TODO list to forbid 
> unaligned access because they should not happen on any device we currently 
> emulate.
> Although, I am not aware of any issue other than the guest would shoot itself 
> in the foot if this happens.
>> So if it is ok with you I will keep that check and discuss it with Rahul
>> when he is back. I will add a comment in the code to make that clear.
> I am OK with it.
> [...]
>>> Throughout this series I haven't been able to spot where the HAS_VPCI
>>> Kconfig symbol would get selected. Hence I cannot tell whether all of
>>> this is Arm64-specific. Otherwise I wonder whether size 8 actually
>>> can occur on Arm32.
>> Dabt.size could be 3 even on ARM32 but we should not allow 64bit
>> access on mmio regions on arm32.
> Hmmm... Looking at the Armv7 and Armv8 spec, ldrd/strd (64-bit read) would 
> not present a valid ISV. So I think it is not be possible to have dabt.size = 
> 3 for 32-bit domain. But I agree we probably want to harden the code.
>> So I will surround this code with ifdef CONFIG_ARM_64 and add a test
>> for len > 4 to prevent this case on 32bit.
>> To be completely right we should disable this also for 32bit guests but
>> this change would be a bit more invasive.
> I think the following should be sufficient:
> if ( is_domain_32bit_domain() && len > 4 )
>  return ...;

With the last request from Roger to use the function implemented in 
arch/x86/hw/io.c, the function will move to vpci.h so using is_32bit_domain 
will not be possible without ifdefery CONFIG_ARM.
Also I have no access to the domain there.

So the best I can do for now would be something like:
#ifdef CONFIG_ARM_32
If (len == 8)
    return false

A 32bit guest on 64bit xen would not be checked.

Would that be ok for now ?

I could add a comment in the code to warn about the limitation.


> Cheers,
> -- 
> Julien Grall



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