From mboxrd@z Thu Jan  1 00:00:00 1970
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v5 1/1] Add mmio_hole_size
Date: Tue, 30 Sep 2014 11:36:49 -0400
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To: George Dunlap <dunlapg@umich.edu>
Cc: Ian Campbell <ian.campbell@citrix.com>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Ian Jackson <ian.jackson@eu.citrix.com>, Don Slutz <dslutz@verizon.com>, "xen-devel@lists.xen.org" <xen-devel@lists.xen.org>, Jan Beulich <jbeulich@suse.com>
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On 09/30/2014 09:22 AM, George Dunlap wrote:
> On Tue, Sep 30, 2014 at 2:27 AM, Boris Ostrovsky
> <boris.ostrovsky@oracle.com> wrote:
>>> +    if ( mmio_hole_size )
>>> +    {
>>> +        uint64_t max_ram_below_4g = (1ULL << 32) - mmio_hole_size;
>>> +
>>> +        if ( max_ram_below_4g > HVM_BELOW_4G_MMIO_START )
>>> +        {
>>> +            printf("max_ram_below_4g=0x"PRIllx
>>> +                   " too big for mmio_hole_size=0x"PRIllx
>>> +                   " has been ignored.\n",
>>> +                   PRIllx_arg(max_ram_below_4g),
>>> +                   PRIllx_arg(mmio_hole_size));
>>> +        }
>>
>> Do you need to check whether the hole is too large?
>>
>> Here and in the toolstack.
> How large is too large?  I've seen real machines with a 3GiB memory hole...


But if mmio_hole_size is set to, say, 4GB we can't expect anything good, 
right? I don't know what the reasonable upper limit on it should be but 
it seems to me we need one. Especially given that it's a uint64_t.

-boris