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Donenfeld" , , , , , , , , , , , , References: <20240418121249.42380-1-Jason@zx2c4.com> <20240418121249.42380-3-Jason@zx2c4.com> Content-Language: en-US From: "Landge, Sudan" In-Reply-To: <20240418121249.42380-3-Jason@zx2c4.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: EX19D032UWA002.ant.amazon.com (10.13.139.81) To EX19D036EUC002.ant.amazon.com (10.252.61.191) On 18/04/2024 13:12, Jason A. Donenfeld wrote: > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > From: Sudan Landge > > Virtual Machine Generation ID driver was introduced in commit > af6b54e2b5ba ("virt: vmgenid: notify RNG of VM fork and supply > generation ID"), as an ACPI only device. > > VMGenID specification http://go.microsoft.com/fwlink/?LinkId=260709 > defines a mechanism for the BIOS/hypervisors to communicate to the > virtual machine that it is executed with a different configuration (e.g. > snapshot execution or creation from a template). The guest operating > system can use the notification for various purposes such as > re-initializing its random number generator etc. > > As per the specs, hypervisor should provide a globally unique > identified, or GUID via ACPI. > > This patch tries to mimic the mechanism to provide the same > functionality which is for a hypervisor/BIOS to notify the virtual > machine when it is executed with a different configuration. > > As part of this support the devicetree bindings requires the hypervisors > or BIOS to provide a memory address which holds the GUID and an IRQ > which is used to notify when there is a change in the GUID. The memory > exposed in the DT should follow the rules defined in the vmgenid spec > mentioned above. > > Reason for this change: Chosing ACPI or devicetree is an intrinsic part > of an hypervisor design. Without going into details of why a hypervisor > would chose DT over ACPI, we would like to highlight that the > hypervisors that have chose devicetree and now want to make use of the > vmgenid functionality cannot do so today because vmgenid is an ACPI only > device. This forces these hypervisors to change their design which > could have undesirable impacts on their use-cases, test-scenarios etc. > > The point of vmgenid is to provide a mechanism to discover a GUID when > the execution state of a virtual machine changes and the simplest way to > do it is pass a memory location and an interrupt via devicetree. It > would complicate things unnecessarily if instead of using devicetree, we > try to implement a new protocol or modify other protocols to somehow > provide the same functionility. > > We believe that adding a devicetree binding for vmgenid is a simpler, > better alternative to provide the same functionality and will allow such > hypervisors as mentioned above to continue using devicetree. > > More references to the vmgenid specs are found below. > > Signed-off-by: Sudan Landge > Reviewed-by: Rob Herring > Reviewed-by: Alexander Graf > Link: https://www.qemu.org/docs/master/specs/vmgenid.html > Link: https://learn.microsoft.com/en-us/windows/win32/hyperv_v2/virtual-machine-generation-identifier > Signed-off-by: Jason A. Donenfeld > --- > .../bindings/rng/microsoft,vmgenid.yaml | 49 +++++++++++++++++++ > MAINTAINERS | 1 + > 2 files changed, 50 insertions(+) > create mode 100644 Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml > > diff --git a/Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml b/Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml > new file mode 100644 > index 000000000000..8f20dee93e7e > --- /dev/null > +++ b/Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml > @@ -0,0 +1,49 @@ > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) > +%YAML 1.2 > +--- > +$id: http://devicetree.org/schemas/rng/microsoft,vmgenid.yaml# > +$schema: http://devicetree.org/meta-schemas/core.yaml# > + > +title: Virtual Machine Generation ID > + > +maintainers: > + - Jason A. Donenfeld > + > +description: > + Firmwares or hypervisors can use this devicetree to describe an > + interrupt and a shared resource to inject a Virtual Machine Generation ID. > + Virtual Machine Generation ID is a globally unique identifier (GUID) and > + the devicetree binding follows VMGenID specification defined in > + http://go.microsoft.com/fwlink/?LinkId=260709. > + > +properties: > + compatible: > + const: microsoft,vmgenid > + > + reg: > + description: > + Specifies a 16-byte VMGenID in endianness-agnostic hexadecimal format. > + maxItems: 1 > + > + interrupts: > + description: > + Interrupt used to notify that a new VMGenID is available. > + maxItems: 1 > + > +required: > + - compatible > + - reg > + - interrupts > + > +additionalProperties: false > + > +examples: > + - | > + #include > + rng@80000000 { > + compatible = "microsoft,vmgenid"; > + reg = <0x80000000 0x1000>; > + interrupts = ; > + }; > + > +... > diff --git a/MAINTAINERS b/MAINTAINERS > index aa3b947fb080..c84ac9258a48 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -18463,6 +18463,7 @@ M: "Theodore Ts'o" > M: Jason A. Donenfeld > S: Maintained > T: git https://git.kernel.org/pub/scm/linux/kernel/git/crng/random.git > +F: Documentation/devicetree/bindings/rng/microsoft,vmgenid.yaml > F: drivers/char/random.c > F: drivers/virt/vmgenid.c > > -- > 2.44.0 > Since I am on leave, looping in Babis to review/verify the patches.