From: Arianna Avanzini <avanzini.arianna@gmail.com>
To: Ian Campbell <Ian.Campbell@eu.citrix.com>
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
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 [thread overview]
Message-ID: <5349056E.7050008@gmail.com> (raw)
In-Reply-To: <1397051683.6275.71.camel@kazak.uk.xensource.com>
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
*/
next prev parent reply other threads:[~2014-04-12 9:20 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-06 23:31 [PATCH v5 0/8] Implement the XEN_DOMCTL_memory_mapping hypercall for ARM Arianna Avanzini
2014-04-06 23:31 ` [PATCH v5 1/8] arch, arm: domain build: let dom0 access I/O memory of mapped devices Arianna Avanzini
2014-04-06 23:31 ` [PATCH v5 2/8] arch, arm: add consistency check to REMOVE p2m changes Arianna Avanzini
2014-04-07 11:05 ` Julien Grall
2014-04-09 13:39 ` Ian Campbell
2014-04-22 19:27 ` Julien Grall
2014-04-06 23:31 ` [PATCH v5 3/8] arch, arm: let map_mmio_regions() take pfn as parameters Arianna Avanzini
2014-04-07 14:56 ` Julien Grall
2014-04-09 13:54 ` Ian Campbell
2014-04-12 9:20 ` Arianna Avanzini [this message]
2014-04-06 23:31 ` [PATCH v5 4/8] arch, x86: check if mapping exists before memory_mapping removes it Arianna Avanzini
2014-04-06 23:31 ` [PATCH v5 5/8] xen, common: add the XEN_DOMCTL_memory_mapping hypercall Arianna Avanzini
2014-04-07 7:55 ` Jan Beulich
2014-04-09 14:03 ` Ian Campbell
2014-04-06 23:31 ` [PATCH v5 6/8] tools, libxl: parse optional start gfn from the iomem config option Arianna Avanzini
2014-04-09 14:10 ` Ian Campbell
2014-04-06 23:31 ` [PATCH v5 7/8] tools, libxl: add helpers to establish if guest is auto-translated Arianna Avanzini
2014-04-06 23:32 ` [PATCH v5 8/8] tools, libxl: handle the iomem parameter with the memory_mapping hcall Arianna Avanzini
2014-04-09 14:25 ` Ian Campbell
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