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Date: Tue, 05 Nov 2013 13:27:57 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] extend limit of physical sections number
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To: Peter Maydell <peter.maydell@linaro.org>
Cc: Amos Kong <akong@redhat.com>, QEMU Developers <qemu-devel@nongnu.org>, Anthony Liguori <anthony@codemonkey.ws>

Il 05/11/2013 13:23, Peter Maydell ha scritto:
>>> >> This looks really weird. Why should the memory subsystem
>>> >> care whether we're using TCG or KVM or Xen?
>> >
>> > Because only TCG stores the section number in the low bits of the iotlb
>> > entry.  This is exactly what is explained in the comments.
> So presumably we still crash if there are more than
> 32 virtio-blk disks on TCG (and indeed if more than 256
> on KVM)? That doesn't seem very satisfactory...

It isn't, do you have any idea on how to make the threshold equal for
TCG and KVM?

I guess the code could be made clearer like this:

    assert (... < SHRT_MAX);
    if (tcg_enabled()) {
        /* TCG has a stricter limit due to iotlb etc. etc. */
        assert (... < TARGET_PAGE_SIZE);
    }

but that's pretty much it...

Paolo