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Date: Fri, 24 May 2013 14:58:22 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 15/30] memory: add address_space_valid
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: David Gibson <david@gibson.dropbear.id.au>, qemu-devel@nongnu.org, jan.kiszka@gmail.com

Il 24/05/2013 12:52, Peter Maydell ha scritto:
> On 24 May 2013 09:02, Paolo Bonzini <pbonzini@redhat.com> wrote:
>> Il 23/05/2013 20:04, Peter Maydell ha scritto:
>>> Shouldn't we be calling the MemoryRegionOps
>>> accepts() callback here? What about access alignment constraints
>>> and access size restrictions?
>>
>> Yes, we should.
>>
>>> What if the validity of the range
>>> changes between the time you asked and when you actually do the
>>> access?
>>
>> If that's a concern, you shouldn't use this API, you should just do the
>> access and rely on the return value of address_space_rw & friends.
> 
> So when *is* it a good idea to use this API? In real
> hardware you don't usually get a "tell me whether this
> access would succeed if I did it" bus operation -- you
> just do the operation and the memory transaction either
> succeeds or it doesn't. Are we modelling something that
> really exists in hardware on spapr here?

Well, sPAPR is not hardware. :)  It is a paravirtualized interface.

Anyhow, I can eliminate all the references to unassigned and basically
do this:

bool address_space_access_valid(AddressSpace *as, hwaddr addr, int len, bool is_write)
{
    MemoryRegionSection *section;
    hwaddr l, xlat;

    while (len > 0) {
        l = len;
        section = address_space_translate(as, addr, &xlat, &l, is_write);
        if (!memory_access_is_direct(section->mr, is_write)) {
            l = memory_access_size(l, addr);
            if (!memory_region_access_valid(section->mr, addr1, l) {
                return false;
            }
        }

        len -= l;
        addr += l;
    }
    return true;
}

It requires some more changes however.  I'll drop this patch.  If it's okay
for you, I'll send a pull request up to "memory: clean up phys_page_find"
and go on with the next series.

Paolo