From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 3/8] xen/arm: Implement p2m_type_t as an enum Date: Thu, 05 Dec 2013 16:01:51 +0000 Message-ID: <52A0A36F.7070908@linaro.org> References: <1386258131-755-1-git-send-email-julien.grall@linaro.org> <1386258131-755-4-git-send-email-julien.grall@linaro.org> <1386258750.20047.84.camel@kazak.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta4.messagelabs.com ([85.158.143.247]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1VobNF-0005kM-VF for xen-devel@lists.xenproject.org; Thu, 05 Dec 2013 16:01:58 +0000 Received: by mail-ea0-f172.google.com with SMTP id q10so11438781ead.31 for ; Thu, 05 Dec 2013 08:01:55 -0800 (PST) In-Reply-To: <1386258750.20047.84.camel@kazak.uk.xensource.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ian Campbell Cc: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com, patches@linaro.org List-Id: xen-devel@lists.xenproject.org On 12/05/2013 03:52 PM, Ian Campbell wrote: > On Thu, 2013-12-05 at 15:42 +0000, Julien Grall wrote: >> Until now, Xen doesn't know the type of the page (ram, foreign page, mmio,...). >> Introduce p2m_type_t with basic types: >> - p2m_invalid: Nothing is mapped here > > Do we really need this? Is it not equivalent to not setting the present > bit? I see x86 has the same type though -- Tim can you explain why. We need a default value when Xen retrieves the p2m type. I don't think we can assume that p2m_ram_rw (or any other type) is used by default. > Since the avail bits in the p2m pte are in pretty short supply I think > we can avoid unnecessary types. I plan to use directly the decimal value. So we can store up to 16 values. >> - p2m_ram_rw: Normal read/write guest RAM >> - p2m_ram_ro: Read-only guest RAM >> - p2m_mmio_direct: Read/write mapping of device memory >> - p2m_map_foreign: RAM page from foreign guest > > Is there no need for an entry for a grant mapping (and a ro > counterpart)? Hmmm .. actually grant table is mapped as RAM (so read/write and execute). Do we want to allow code execution from grant-mapping page? If not, then we will need to introduce specific p2m type from grant-mapping. -- Julien Grall