[pve-devel] [PATCH qemu-server 1/1] snapshot: prohibit snapshot with ram if vm has a passthrough pci device

[Fabian Grünbichler]

On March 19, 2024 4:08 pm, Hannes Duerr wrote:
> When a snapshot is created with RAM, qemu attempts to save not only the
> RAM content, but also the internal state of the PCI devices.
> 
> However, as not all drivers support this, this can lead to the device
> drivers in the VM not being able to handle the saved state during the
> restore/rollback and in conclusion the VM might crash. For this reason,
> we now generally prohibit snapshots with RAM for VMs with passthrough
> devices.
> 
> In the future, this prohibition can of course be relaxed for individual
> drivers that we know support it, such as the vfio driver
> 
> Signed-off-by: Hannes Duerr <h.duerr at proxmox.com>
> ---
>  PVE/API2/Qemu.pm | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/PVE/API2/Qemu.pm b/PVE/API2/Qemu.pm
> index 40b6c30..0acd1c7 100644
> --- a/PVE/API2/Qemu.pm
> +++ b/PVE/API2/Qemu.pm
> @@ -5101,6 +5101,16 @@ __PACKAGE__->register_method({
>  	die "unable to use snapshot name 'pending' (reserved name)\n"
>  	    if lc($snapname) eq 'pending';
>  
> +	if ($param->{vmstate}) {
> +	    my $conf = PVE::QemuConfig->load_config($vmid);
> +
> +	    for my $key (keys %$conf) {
> +		next if $key !~ /^hostpci\d+/;
> +		die "cannot snapshot VM with RAM due to passed-through PCI device(s), which lack"
> +		    ." the possibility to save/restore their internal state\n";
> +	    }
> +	}

isn't the same also true of other local resources (e.g., passed-through
USB?)?

maybe we could find a way to unify the checks we do for live migration
(PVE::QemuServer::check_local_resources), since that is almost the same
code inside Qemu as a stateful snapshot+rollback?

(not opposed to applying this before that happens though, just a
question in general..)

> +
>  	my $realcmd = sub {
>  	    PVE::Cluster::log_msg('info', $authuser, "snapshot VM $vmid: $snapname");
>  	    PVE::QemuConfig->snapshot_create($vmid, $snapname, $param->{vmstate},
> -- 
> 2.39.2
> 
> 
> 
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