Re: [Qemu-devel] [PATCH v2 3/4] nvdimm: add a boolean option "restrict"

[Stefan Hajnoczi]

On Tue, Jun 06, 2017 at 03:22:28PM +0800, Haozhong Zhang wrote:
> If a vNVDIMM device is not backed by a DAX device and its "restrict"
> option is enabled, bit 3 of state flags in its region mapping
> structure will be set, in order to notify the guest of the lack of
> write persistence guarantee. Once this bit is set, the guest OS may
> mark the vNVDIMM device as read-only.
> 
> This option is disabled by default for backwards compatibility. It's
> recommended to enable for the formal usage.

Good idea.  I think the following is cleaner:

DEFINE_PROP_ON_OFF_AUTO("readonly") on the 'nvdimm' device.  The
following states are available:

 * 'on' - ACPI_NFIT_MEM_NOT_ARMED is set
 * 'off' - ACPI_NFIT_MEM_NOT_ARMED is clear
 * 'auto' - ACPI_NFIT_MEM_NOT_ARMED set if backend is not persistent

This new property defaults to 'auto'.  Machine types older than
pc-i440fx-2.10 and pc-q35-2.10 default to 'on'.

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