Add CLI flag --gpu=drm|venus|software to support various GPU virtualization modes

vDRM is great, but not supported everywhere yet, so on some machines the only way
to get GPU acceleration is via Venus. Also, make it possible to use software
rendering only while still having working cross-domain Wayland.

Signed-off-by: Val Packett <[email protected]>

Author: valpackett

crates/muvm/src/bin/muvm.rs

@@ -11,7 +11,8 @@ use krun_sys::{
     krun_add_disk, krun_add_virtiofs2, krun_add_vsock_port, krun_add_vsock_port2, krun_create_ctx,
     krun_set_env, krun_set_gpu_options2, krun_set_log_level, krun_set_passt_fd, krun_set_root,
     krun_set_vm_config, krun_set_workdir, krun_start_enter, VIRGLRENDERER_DRM,
-    VIRGLRENDERER_THREAD_SYNC, VIRGLRENDERER_USE_ASYNC_FENCE_CB, VIRGLRENDERER_USE_EGL,
+    VIRGLRENDERER_NO_VIRGL, VIRGLRENDERER_RENDER_SERVER, VIRGLRENDERER_THREAD_SYNC,
+    VIRGLRENDERER_USE_ASYNC_FENCE_CB, VIRGLRENDERER_USE_EGL, VIRGLRENDERER_VENUS,
 };
 use log::debug;
 use muvm::cli_options::options;
@@ -184,8 +185,14 @@ fn main() -> Result<ExitCode> {
                 .context("Failed to configure the number of vCPUs and/or the amount of RAM");
         }
 
+        let virgl_mode = match options.gpu_mode.unwrap_or_default() {
+            muvm::cli_options::GpuMode::Drm => VIRGLRENDERER_DRM,
+            muvm::cli_options::GpuMode::Venus => VIRGLRENDERER_VENUS | VIRGLRENDERER_RENDER_SERVER,
+            muvm::cli_options::GpuMode::Software => 0,
+        };
         let virgl_flags = VIRGLRENDERER_USE_EGL
-            | VIRGLRENDERER_DRM
+            | VIRGLRENDERER_NO_VIRGL /* Legacy method that we don't support; interferes with software-only mode */
+            | virgl_mode
             | VIRGLRENDERER_THREAD_SYNC
             | VIRGLRENDERER_USE_ASYNC_FENCE_CB;
         // SAFETY: Safe as no pointers involved.
@@ -436,6 +443,10 @@ fn main() -> Result<ExitCode> {
         env.insert("XAUTHORITY".to_owned(), xauthority);
     }
 
+    if options.gpu_mode == Some(muvm::cli_options::GpuMode::Venus) {
+        env.insert("MESA_LOADER_DRIVER_OVERRIDE".to_owned(), "zink".to_owned());
+    }
+
     let krun_config = KrunBaseConfig {
         config: KrunConfig {
             args: muvm_guest_args,

crates/muvm/src/cli_options.rs

@@ -7,6 +7,29 @@ use bpaf::{any, construct, long, positional, OptionParser, Parser};
 use crate::types::MiB;
 use crate::utils::launch::Emulator;
 
+#[derive(Debug, Clone, Copy, Default, PartialEq)]
+pub enum GpuMode {
+    #[default]
+    Drm,
+    Venus,
+    Software,
+}
+
+impl std::str::FromStr for GpuMode {
+    type Err = String;
+    fn from_str(s: &str) -> Result<Self, String>
+    where
+        Self: Sized,
+    {
+        match s {
+            "drm" => Ok(GpuMode::Drm),
+            "venus" => Ok(GpuMode::Venus),
+            "software" => Ok(GpuMode::Software),
+            x => Err(format!("Expected drm|venus|software, got '{x}'")),
+        }
+    }
+}
+
 #[derive(Clone, Debug)]
 pub struct Options {
     pub cpu_list: Vec<Range<u16>>,
@@ -19,6 +42,7 @@ pub struct Options {
     pub interactive: bool,
     pub tty: bool,
     pub privileged: bool,
+    pub gpu_mode: Option<GpuMode>,
     pub publish_ports: Vec<String>,
     pub emulator: Option<Emulator>,
     pub init_commands: Vec<PathBuf>,
@@ -125,6 +149,10 @@ pub fn options() -> OptionParser<Options> {
         This notably does not allow root access to the host fs.",
         )
         .switch();
+    let gpu_mode = long("gpu-mode")
+        .help("Use the given GPU virtualization method")
+        .argument::<GpuMode>("drm|venus|software")
+        .optional();
     let publish_ports = long("publish")
         .short('p')
         .help(
@@ -169,6 +197,7 @@ pub fn options() -> OptionParser<Options> {
         interactive,
         tty,
         privileged,
+        gpu_mode,
         publish_ports,
         emulator,
         init_commands,