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arch: riscv64: Expose host extension set to guest via FDT

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The set of extensions supported by a RISC-V system needs to be exposed
to the guest - currently that is a fixed, minimal set of extensions.
These extensions are not sufficient to boot Ubuntu 25.10 which now has a
mininimum requirement of RVA23S64 (which is a minimum set of extensions
that make sense for server use cases.)

The easiest way to convey the extensions that the guest should use is to
copy those that the host kernel understands (and thus includes in the
/proc/cpuinfo) data.

However since nested virtualisation is not currently possible - exclude
the "H" (Hypervisor) extension from the list of short (single letter)
extensions.

Signed-off-by: Rob Bradford <rbradford@rivosinc.com>
This commit is contained in:
Rob Bradford
2025-11-11 15:48:42 +00:00
parent d586c844de
commit 063aa4b7d5
2 changed files with 61 additions and 3 deletions
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7
arch/src/riscv64/fdt.rs
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@@ -65,6 +65,7 @@ pub fn create_fdt<T: DeviceInfoForFdt + Clone + Debug, S: ::std::hash::BuildHash
guest_mem: &GuestMemoryMmap,
cmdline: &str,
num_vcpu: u32,
isa_string: &str,
device_info: &HashMap<(DeviceType, String), T, S>,
aia_device: &Arc<Mutex<dyn Vaia>>,
initrd: &Option<InitramfsConfig>,
@@ -84,7 +85,7 @@ pub fn create_fdt<T: DeviceInfoForFdt + Clone + Debug, S: ::std::hash::BuildHash
// Properties
fdt.property_u32("#address-cells", ADDRESS_CELLS)?;
fdt.property_u32("#size-cells", SIZE_CELLS)?;
create_cpu_nodes(&mut fdt, num_vcpu)?;
create_cpu_nodes(&mut fdt, num_vcpu, isa_string)?;
create_memory_node(&mut fdt, guest_mem)?;
create_chosen_node(&mut fdt, cmdline, initrd)?;
create_aia_node(&mut fdt, aia_device)?;
@@ -108,7 +109,7 @@ pub fn write_fdt_to_memory(fdt_final: Vec<u8>, guest_mem: &GuestMemoryMmap) -> R
}
// Following are the auxiliary function for creating the different nodes that we append to our FDT.
fn create_cpu_nodes(fdt: &mut FdtWriter, num_cpus: u32) -> FdtWriterResult<()> {
fn create_cpu_nodes(fdt: &mut FdtWriter, num_cpus: u32, isa_string: &str) -> FdtWriterResult<()> {
// See https://elixir.bootlin.com/linux/v6.10/source/Documentation/devicetree/bindings/riscv/cpus.yaml
let cpus = fdt.begin_node("cpus")?;
// As per documentation, on RISC-V 64-bit systems value should be set to 1.
@@ -123,7 +124,7 @@ fn create_cpu_nodes(fdt: &mut FdtWriter, num_cpus: u32) -> FdtWriterResult<()> {
fdt.property_string("device_type", "cpu")?;
fdt.property_string("compatible", "riscv")?;
fdt.property_string("mmu-type", "sv48")?;
fdt.property_string("riscv,isa", "rv64imafdc_smaia_ssaia")?;
fdt.property_string("riscv,isa", isa_string)?;
fdt.property_string("status", "okay")?;
fdt.property_u32("reg", cpu_index)?;
fdt.property_u32("phandle", CPU_BASE_PHANDLE + cpu_index)?;