checkpoint: linux getting to user-space, but crashing in user-space

Problem is that FPU access in Linux or Linux user-space causes
exceptions *in Linux*, which is weird for two reasons:

1. We have the FPU enabled for QEMU in seL4 so I would think that the
   guest would have FPU access as well.
2. Why is an illegal instruction exception that happened *within Linux*
   being handled by Linux instead of the VMM?

build.zig

@@ -77,7 +77,7 @@ pub fn build(b: *std.Build) void {
             "-Werror",
             "-Wno-unused-function",
             "-mstrict-align",
-            "-fno-sanitize=undefined", // @ivanv: ideally we wouldn't have to turn off UBSAN
+            // "-fno-sanitize=undefined", // @ivanv: ideally we wouldn't have to turn off UBSAN
         }
     });
 

examples/simple/board/qemu_virt_riscv64/linux_config

@@ -344,14 +344,11 @@ CONFIG_RISCV_ISA_C=y
 CONFIG_RISCV_ISA_SVNAPOT=y
 CONFIG_RISCV_ISA_SVPBMT=y
 CONFIG_TOOLCHAIN_HAS_V=y
-CONFIG_RISCV_ISA_V=y
-CONFIG_RISCV_ISA_V_DEFAULT_ENABLE=y
-CONFIG_RISCV_ISA_V_UCOPY_THRESHOLD=768
 # CONFIG_RISCV_ISA_ZICBOM is not set
 # CONFIG_RISCV_ISA_ZICBOZ is not set
 CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE=y
 CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI=y
-CONFIG_FPU=y
+# CONFIG_FPU is not set
 CONFIG_IRQ_STACKS=y
 CONFIG_THREAD_SIZE_ORDER=2
 CONFIG_RISCV_MISALIGNED=y
@@ -604,8 +601,6 @@ CONFIG_HAVE_PREEMPT_DYNAMIC_KEY=y
 CONFIG_ARCH_WANT_LD_ORPHAN_WARN=y
 CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC=y
 CONFIG_ARCH_SUPPORTS_PAGE_TABLE_CHECK=y
-CONFIG_DYNAMIC_SIGFRAME=y
-CONFIG_ARCH_HAS_KERNEL_FPU_SUPPORT=y
 
 #
 # GCOV-based kernel profiling

examples/simple/board/qemu_virt_riscv64/overlay.dts

@@ -14,10 +14,52 @@
         status = "disabled";
     };
 
+    soc {
+        rtc@101000 {
+            status = "disabled";
+        };
+
+        pci@30000000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10008000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10007000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10006000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10005000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10004000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10003000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10002000 {
+            status = "disabled";
+        };
+
+        virtio_mmio@10001000 {
+            status = "disabled";
+        };
+    };
+
     chosen {
         stdout-path = "/uart@10000000";
-        bootargs = "console=ttyS0 loglevel=8 earlycon=ns16550a,0x10000000";
+        bootargs = "console=ttyS0 loglevel=8 earlycon=ns16550a,0x10000000 no4lvl";
         linux,initrd-start = <0x8c000000>;
-        linux,initrd-end = <0x8d000000>;
+        linux,initrd-end = <0x8e000000>;
     };
 };

examples/simple/board/qemu_virt_riscv64/simple.system

@@ -9,7 +9,7 @@
 
     <memory_region name="serial" size="0x1_000" phys_addr="0x10000000" />
 
-    <protection_domain name="VMM" priority="254">
+    <protection_domain name="VMM" priority="254" stack_size="0x2000">
         <program_image path="vmm.elf" />
         <map mr="guest_ram" vaddr="0x80000000" perms="rw" setvar_vaddr="guest_ram_vaddr" />
         <virtual_machine name="linux">

examples/simple/build.zig

@@ -71,7 +71,7 @@ const ConfigOptions = enum {
     benchmark
 };
 
-pub fn build(b: *std.Build) void {
+pub fn build(b: *std.Build) !void {
     const optimize = b.standardOptimizeOption(.{});
 
     // Getting the path to the Microkit SDK before doing anything else
@@ -177,15 +177,24 @@ pub fn build(b: *std.Build) void {
     const linux_image_path = b.fmt("board/{s}/linux", .{ microkit_board });
     const kernel_image_arg = b.fmt("-DGUEST_KERNEL_IMAGE_PATH=\"{s}\"", .{ linux_image_path });
 
+    var prng = std.Random.DefaultPrng.init(blk: {
+        var seed: u64 = undefined;
+        try std.posix.getrandom(std.mem.asBytes(&seed));
+        break :blk seed;
+    });
+    const rand = prng.random();
+
     const initrd_image_path = b.fmt("board/{s}/rootfs.cpio.gz", .{ microkit_board });
     const initrd_image_arg = b.fmt("-DGUEST_INITRD_IMAGE_PATH=\"{s}\"", .{ initrd_image_path });
     const dtb_image_arg = b.fmt("-DGUEST_DTB_IMAGE_PATH=\"{s}\"", .{ b.getInstallPath(.prefix, "linux.dtb") });
+    const random_arg = b.fmt("-DRANDOM=\"{}\"", .{ rand.int(usize) });
     guest_images.addCSourceFile(.{
         .file = libvmm_dep.path("tools/package_guest_images.S"),
         .flags = &.{
             kernel_image_arg,
             dtb_image_arg,
             initrd_image_arg,
+            random_arg,
             "-x",
             "assembler-with-cpp",
         }

examples/simple/vmm.c

@@ -123,6 +123,7 @@ void init(void) {
         return;
     }
     success = virq_register(GUEST_VCPU_ID, SERIAL_IRQ, &serial_ack, NULL);
+    assert(success);
     /* Just in case there is already an interrupt available to handle, we ack it here. */
     microkit_irq_ack(SERIAL_IRQ_CH);
     /* Finally start the guest */
@@ -132,10 +133,10 @@ void init(void) {
 void notified(microkit_channel ch) {
     switch (ch) {
         case SERIAL_IRQ_CH: {
-            bool success = virq_inject(GUEST_VCPU_ID, SERIAL_IRQ);
-            if (!success) {
-                LOG_VMM_ERR("IRQ %d dropped on vCPU %d\n", SERIAL_IRQ, GUEST_VCPU_ID);
-            }
+            // bool success = virq_inject(GUEST_VCPU_ID, SERIAL_IRQ);
+            // if (!success) {
+            //     LOG_VMM_ERR("IRQ %d dropped on vCPU %d\n", SERIAL_IRQ, GUEST_VCPU_ID);
+            // }
             break;
         }
         default: