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From: Gerd Hoffmann <kraxel@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	Marcel Apfelbaum <marcel@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	qemu-devel@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>
Subject: Re: [Qemu-devel] Default for phys-addr-bits? (was Re: [PATCH 4/5] x86: Allow physical address bits to be set)
Date: Thu, 23 Jun 2016 10:40:03 +0200	[thread overview]
Message-ID: <1466671203.26189.35.camel@redhat.com> (raw)
In-Reply-To: <20160623024400-mutt-send-email-mst@redhat.com>

  Hi,

> > Well the crash of guest phys bits > host phys bits, should be easy to
> > reproduce by booting a 65GB guest on a 64GB RAM + 2GB swap host with
> > 36 host phys bits using the upstream qemu that forces the guest phys
> > bits to 40.
> 
> So you supply more RAM than host can address, and guest crashes?

Yep.  The only reason we don't see this happening in practice is that
it's probably next to impossible to find a machine which has (a) only 36
physical address lines and (b) allows to plug that much RAM.

> Why are we worried about it?

It's more a issue with pci ressources.  In theory seabios/edk2 could go
figure how big the physical address space is, then map 64bit pci bars as
high as possible, thereby making stuff like etc/reserved-memory-end in
fw_cfg unnecessary.

But with qemu saying 40 phys bits are available even if they are not
this approach isn't going to fly ...

cheers,
  Gerd

  reply	other threads:[~2016-06-23  8:40 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-16 17:12 [Qemu-devel] [PATCH 0/5] x86: Physical address limit patches Dr. David Alan Gilbert (git)
2016-06-16 17:12 ` [Qemu-devel] [PATCH 1/5] BIT_RANGE convenience macro Dr. David Alan Gilbert (git)
2016-06-16 17:23   ` Paolo Bonzini
2016-06-16 17:24     ` Dr. David Alan Gilbert
2016-06-16 18:01   ` Peter Maydell
2016-06-16 18:05     ` Paolo Bonzini
2016-06-20 14:11     ` Dr. David Alan Gilbert
2016-06-20 14:17       ` Peter Maydell
2016-06-16 17:12 ` [Qemu-devel] [PATCH 2/5] x86: Mask mtrr mask based on CPU physical address limits Dr. David Alan Gilbert (git)
2016-06-16 19:59   ` Eduardo Habkost
2016-06-17  8:23     ` Dr. David Alan Gilbert
2016-06-17 12:13     ` Paolo Bonzini
2016-06-16 17:12 ` [Qemu-devel] [PATCH 3/5] x86: fill high bits of mtrr mask Dr. David Alan Gilbert (git)
2016-06-16 20:14   ` Eduardo Habkost
2016-06-17  7:47     ` Paolo Bonzini
2016-06-17 12:46       ` Eduardo Habkost
2016-06-17 13:01         ` Paolo Bonzini
2016-06-17 13:41           ` Eduardo Habkost
2016-06-17 14:25             ` Paolo Bonzini
2016-06-17 15:27               ` Eduardo Habkost
2016-06-17 15:29                 ` Paolo Bonzini
2016-06-17 15:35                   ` Eduardo Habkost
2016-06-17 13:51           ` Dr. David Alan Gilbert
2016-06-17 14:19             ` Paolo Bonzini
2016-06-17  8:53     ` Dr. David Alan Gilbert
2016-06-16 17:12 ` [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set Dr. David Alan Gilbert (git)
2016-06-16 17:26   ` Paolo Bonzini
2016-06-16 18:09     ` Eduardo Habkost
2016-06-16 20:24   ` Eduardo Habkost
2016-06-17  8:15     ` Dr. David Alan Gilbert
2016-06-17  8:43       ` Paolo Bonzini
2016-06-17  9:17         ` Gerd Hoffmann
2016-06-17  9:52           ` Igor Mammedov
2016-06-17 11:20             ` Gerd Hoffmann
2016-06-17 16:20               ` Laszlo Ersek
2016-06-17 16:07             ` Laszlo Ersek
2016-06-19 16:13               ` Marcel Apfelbaum
2016-06-20 10:42                 ` Igor Mammedov
2016-06-20 11:13                   ` Marcel Apfelbaum
2016-06-17  9:37       ` Dr. David Alan Gilbert
2016-06-17  9:54         ` Paolo Bonzini
2016-06-17 13:18       ` Eduardo Habkost
2016-06-17 13:38         ` Paolo Bonzini
2016-06-17 15:19           ` Eduardo Habkost
2016-06-17 15:28             ` Paolo Bonzini
2016-06-17 15:49               ` Eduardo Habkost
2016-06-21 19:44                 ` [Qemu-devel] Default for phys-addr-bits? (was Re: [PATCH 4/5] x86: Allow physical address bits to be set) Eduardo Habkost
2016-06-22 12:41                   ` Paolo Bonzini
2016-06-22 14:24                     ` Andrea Arcangeli
2016-06-22 14:33                       ` Paolo Bonzini
2016-06-22 14:44                         ` Andrea Arcangeli
2016-06-22 14:48                           ` Paolo Bonzini
2016-06-22 15:02                             ` Andrea Arcangeli
2016-06-22 22:44                       ` Michael S. Tsirkin
2016-06-22 23:23                         ` Andrea Arcangeli
2016-06-22 23:45                           ` Michael S. Tsirkin
2016-06-23  8:40                             ` Gerd Hoffmann [this message]
2016-06-23 16:38                               ` Michael S. Tsirkin
2016-06-24  5:55                                 ` Gerd Hoffmann
2016-06-24 23:12                                   ` Michael S. Tsirkin
2016-06-29 16:42                               ` Dr. David Alan Gilbert
2016-06-30  6:10                                 ` Gerd Hoffmann
2016-06-30 10:59                                   ` Dr. David Alan Gilbert
2016-06-30 16:14                                     ` Gerd Hoffmann
2016-06-30 17:12                                       ` Dr. David Alan Gilbert
2016-07-01 19:03                                       ` Dr. David Alan Gilbert
2016-06-22 22:40                     ` Michael S. Tsirkin
2016-06-22 23:15                       ` Andrea Arcangeli
2016-06-19  3:36           ` [Qemu-devel] [PATCH 4/5] x86: Allow physical address bits to be set Michael S. Tsirkin
2016-06-20  7:04             ` Paolo Bonzini
2016-06-17 14:24         ` Marcel Apfelbaum
2016-06-16 17:12 ` [Qemu-devel] [PATCH 5/5] x86: Set physical address bits based on host Dr. David Alan Gilbert (git)
2016-06-17  7:25   ` Igor Mammedov

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