feat(amd64): basic hypervisor detection

src/arch/amd64/root.zig

@@ -18,6 +18,8 @@ pub const Msr = enum(u32) {
     Star = 0xC000_0081,
     /// IA32_LSTAR
     LStar = 0xC000_0082,
+    /// MSR_KVM_SYSTEM_TIME_NEW
+    KvmSystemTimeNew = 0x4B564D01,
 };
 
 pub const IrqFrame = extern struct {
@@ -263,6 +265,7 @@ pub const CpuidRequest = union(enum) {
     extended_features: ExtendedFeaturesSubLeaf,
     brand_string: BrandStringPart,
     power_management_info,
+    hypervisor_id,
 
     pub const ExtendedFeaturesSubLeaf = enum(u32) {
         first = 0,
@@ -285,6 +288,7 @@ pub const CpuidRequest = union(enum) {
             .power_management_info => .{ 0x80000007, 0 },
             .extended_features => |s| .{ 0x7, @intFromEnum(s) },
             .brand_string => |p| .{ @intFromEnum(p), 0 },
+            .hypervisor_id => .{ 0x40000000, 0 },
         };
         return cpuid(leaf, subleaf);
     }
@@ -425,8 +429,50 @@ pub const CpuFeatures = struct {
     brand_string: [48]u8,
 };
 
+pub const HypervisorVendor = enum(u32) {
+    Unknown = 0,
+    KVM = 1,
+};
+
+pub const HypervisorInfo = struct {
+    brand_string: [12]u8,
+    vendor: HypervisorVendor,
+    highest_function: u32,
+};
+
+pub var hypervisor_info: ?HypervisorInfo = null;
 pub var cpu_features: CpuFeatures = undefined;
 
+const known_hypervisors = [_]struct {
+    vendor_string: *const [12:0]u8,
+    vendor: HypervisorVendor,
+}{
+    .{ .vendor_string = "KVMKVMKVM\x00\x00\x00", .vendor = HypervisorVendor.KVM },
+};
+
+fn detect_hypervisor() void {
+    const r = CpuidRequest.execute(.hypervisor_id);
+    var hypervisor_brand: [12]u8 = undefined;
+    std.mem.writeInt(u32, hypervisor_brand[0..4], r.ebx, .little);
+    std.mem.writeInt(u32, hypervisor_brand[4..8], r.ecx, .little);
+    std.mem.writeInt(u32, hypervisor_brand[8..12], r.edx, .little);
+
+    var vendor = HypervisorVendor.Unknown;
+
+    for (known_hypervisors) |h| {
+        if (std.mem.eql(u8, hypervisor_brand[0..], h.vendor_string[0..])) {
+            vendor = h.vendor;
+            break;
+        }
+    }
+
+    hypervisor_info = HypervisorInfo{
+        .brand_string = hypervisor_brand,
+        .vendor = vendor,
+        .highest_function = r.eax,
+    };
+}
+
 pub fn detect_cpu_features() void {
     const vendor_info = CpuidRequest.execute(.vendor_info);
     const max_ext = CpuidRequest.execute(.highest_extended_function).eax;
@@ -445,6 +491,7 @@ pub fn detect_cpu_features() void {
     var smap = false;
     var smep = false;
     var pge = false;
+    var hypervisor = false;
 
     var vendor_string: [12]u8 = undefined;
     var brand_string: [48]u8 = undefined;
@@ -464,6 +511,7 @@ pub fn detect_cpu_features() void {
         pcid = ecx.pcid;
         fxsave = edx.fxsave;
         pge = edx.pge;
+        hypervisor = ecx.hypervisor;
     }
 
     if (max_basic >= 0x7) {
@@ -505,6 +553,10 @@ pub fn detect_cpu_features() void {
         invtsc = edx.invtsc;
     }
 
+    if (hypervisor) {
+        detect_hypervisor();
+    }
+
     cpu_features = .{
         .x2apic = x2apic,
         .five_level_paging = five_level_paging,

src/platform/pc/impl.zig

@@ -34,7 +34,7 @@ pub fn early_init(boot_info: *pl.BootInfo) linksection(b.init) void {
     const f = amd64.cpu_features;
 
     std.log.info("amd64/cpu: {s}", .{&f.brand_string});
-    std.log.info("amd64/cpu: vendor={s} x2apic={} la57={} nx={} pcid={} pge={} smap={} smep={} pdpe1g={} invtsc={} xsave={} fxsave={} tsc-deadline={}", .{
+    std.log.info("amd64/cpu: vendor={s} features={}{}{}{}{}{}{}{}{}{}{}{}", .{
         &f.vendor_string,
         @intFromBool(f.x2apic),
         @intFromBool(f.five_level_paging),
@@ -49,6 +49,10 @@ pub fn early_init(boot_info: *pl.BootInfo) linksection(b.init) void {
         @intFromBool(f.fxsave),
         @intFromBool(f.tsc_deadline),
     });
+
+    if (amd64.hypervisor_info) |h| {
+        std.log.info("amd64/cpu: running on hypervisor {s}", .{@tagName(h.vendor)});
+    }
     _ = boot_info;
 }