From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arianna Avanzini Subject: Re: [PATCH v5 3/8] arch, arm: let map_mmio_regions() take pfn as parameters Date: Sat, 12 Apr 2014 11:20:46 +0200 Message-ID: <5349056E.7050008@gmail.com> References: <1396827120-30617-1-git-send-email-avanzini.arianna@gmail.com> <1396827120-30617-4-git-send-email-avanzini.arianna@gmail.com> <1397051683.6275.71.camel@kazak.uk.xensource.com> Reply-To: Arianna Avanzini Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1397051683.6275.71.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: paolo.valente@unimore.it, keir@xen.org, stefano.stabellini@eu.citrix.com, Ian.Jackson@eu.citrix.com, dario.faggioli@citrix.com, tim@xen.org, xen-devel@lists.xen.org, julien.grall@citrix.com, etrudeau@broadcom.com, JBeulich@suse.com, viktor.kleinik@globallogic.com List-Id: xen-devel@lists.xenproject.org Hello, thank you for your comments, and sorry for the huge delay in replying. On 04/09/2014 03:54 PM, Ian Campbell wrote: > On Mon, 2014-04-07 at 01:31 +0200, Arianna Avanzini wrote: >> - res = map_mmio_regions(d, addr & PAGE_MASK, >> - PAGE_ALIGN(addr + size) - 1, >> - addr & PAGE_MASK); >> + res = map_mmio_regions(d, >> + paddr_to_pfn(addr & PAGE_MASK), >> + paddr_to_pfn_aligned(addr + size - 1), > > > With > +#define paddr_to_pfn_aligned(paddr) paddr_to_pfn(PAGE_ALIGN(paddr)) > > There is a subtle difference here, which is that the "- 1" is now inside > the align. Does this always have the same result? I'm not sure. > > If addr+size == 0x1000 (page aligned) then: > > PAGE_ALIGN(0x10000)-1 = 0x10000-1 = 0xffff > > But > > paddr_to_pfn_aligned(0x10000 - 1) = > paddr_to_pfn(PAGE_ALIGN(0xffff)) = paddr_to_pfn(0x10000) = 0x10 > > The new map_mmio_regions uses pfn_to_paddr which is: > #define pfn_to_paddr(pfn) ((paddr_t)(pfn) << PAGE_SHIFT) > > So with the old code the end address would be 0xffff, while with the new > code it is 0x10<<12 = 0x10000. > > I suspect the implementation of apply_to_p2m_changes is such that it > doesn't actually change anything. Can you confirm that this was your > intention? > It wasn't my intention to change the size of the address range to be mapped, thank you for pointing that out. As far as I can understand, the changes in this patch would let apply_p2m_changes() use one extra address for the mapping; sorry for that. While preparing the patch I saw that, e.g., with addr + size = 0x10000, end_gfn = paddr_to_pfn(PAGE_ALIGN(0x10000) - 1) = paddr_to_pfn(PAGE_ALIGN(0x10000)) - 1 = 0xf and pfn_to_paddr(end_gfn) = 0xf000 which seemed to me to be wrong, as the previous end address was, as you wrote, 0xffff. Instead, if end_gfn = paddr_to_pfn(PAGE_ALIGN(0x10000 - 1)) = 0x10 then pfn_to_paddr(end_gfn) = 0x10000 which I thought lets the needed address range be mapped; however I didn't see what you pointed out, that it also lets one extra address be used for the mapping. > Is the end argument tio map_mmio_regions now intended to be inclusive or > exclusive? As far as I understand, apply_p2m_changes(), which is called by the ARM version of map_mmio_regions(), seems to take it as exclusive, as the mapping is performed while (addr < end_gpaddr). In the x86 version of map_mmio_regions() it is instead intended to be inclusive; sorry for this mismatch, I'll try to make the behavior of the two versions consistent. > This sort of issue can be avoided by using a count instead of > an end in the interface. > Thank you very much for the hint. > Ian. > -- /* * Arianna Avanzini * avanzini.arianna@gmail.com * 73628@studenti.unimore.it */