x86_64: use __cpuid intrinsic

Use the Rust __cpuid and __cpuid_count intrinsics to replace the C
implementation in host_cpuid.c.

These are defined in core, but they are also re-exported in std, despite
being undocumented there due to technical reasons:
https://github.com/rust-lang/rust/pull/57808#issuecomment-457390549

Use the std version for consistency (we don't currently use anything
from core anywhere else in crosvm).

BUG=None
TEST=cargo test -p x86_64
TEST=Boot crosvm on x86_64

Change-Id: Ic7a1094d1b804304a2944f8ee1fe55c5e2db23e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2067159
Reviewed-by: Zach Reizner <zachr@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

4 files changed, 15 insertions, 77 deletions

diff --git a/x86_64/Cargo.toml b/x86_64/Cargo.toml
index e5d5e14..3f5ba3e 100644
--- a/x86_64/Cargo.toml
+++ b/x86_64/Cargo.toml
@@ -3,7 +3,6 @@ name = "x86_64"
 version = "0.1.0"
 authors = ["The Chromium OS Authors"]
 edition = "2018"
-build = "build.rs"
 
 [dependencies]
 arch = { path = "../arch" }
@@ -20,6 +19,3 @@ remain = "*"
 resources = { path = "../resources" }
 sync = { path = "../sync" }
 sys_util = { path = "../sys_util" }
-
-[build-dependencies]
-cc = "=1.0.25"
diff --git a/x86_64/build.rs b/x86_64/build.rs
deleted file mode 100644
index 5f2c1eb..0000000
--- a/x86_64/build.rs
+++ /dev/null
@@ -1,7 +0,0 @@
-// Copyright 2018 The Chromium OS Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-fn main() {
-    cc::Build::new().file("host_cpuid.c").compile("host_cpuid");
-}
diff --git a/x86_64/host_cpuid.c b/x86_64/host_cpuid.c
deleted file mode 100644
index 3230c90..0000000
--- a/x86_64/host_cpuid.c
+++ /dev/null
@@ -1,11 +0,0 @@
-// Copyright 2018 The Chromium OS Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include <stdint.h>
-
-void host_cpuid(uint32_t func, uint32_t func2, uint32_t *pEax,
-                uint32_t *pEbx, uint32_t *pEcx, uint32_t *pEdx) {
-    asm volatile("cpuid" : "=a"(*pEax), "=b"(*pEbx), "=c"(*pEcx), "=d"(*pEdx) :
-                 "0"(func), "2"(func2) : "cc");
-}
diff --git a/x86_64/src/cpuid.rs b/x86_64/src/cpuid.rs
index a42b662..46294b2 100644
--- a/x86_64/src/cpuid.rs
+++ b/x86_64/src/cpuid.rs
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+use std::arch::x86_64::{__cpuid, __cpuid_count};
 use std::fmt::{self, Display};
 use std::result;
 
@@ -28,19 +29,6 @@ impl Display for Error {
     }
 }
 
-// This function is implemented in C because stable rustc does not
-// support inline assembly.
-extern "C" {
-    fn host_cpuid(
-        func: u32,
-        func2: u32,
-        rEax: *mut u32,
-        rEbx: *mut u32,
-        rEcx: *mut u32,
-        rEdx: *mut u32,
-    ) -> ();
-}
-
 // CPUID bits in ebx, ecx, and edx.
 const EBX_CLFLUSH_CACHELINE: u32 = 8; // Flush a cache line size.
 const EBX_CLFLUSH_SIZE_SHIFT: u32 = 8; // Bytes flushed when executing CLFLUSH.
@@ -77,25 +65,19 @@ fn filter_cpuid(
                 }
             }
             2 | 0x80000005 | 0x80000006 => unsafe {
-                host_cpuid(
-                    entry.function,
-                    0,
-                    &mut entry.eax as *mut u32,
-                    &mut entry.ebx as *mut u32,
-                    &mut entry.ecx as *mut u32,
-                    &mut entry.edx as *mut u32,
-                );
+                let result = __cpuid(entry.function);
+                entry.eax = result.eax;
+                entry.ebx = result.ebx;
+                entry.ecx = result.ecx;
+                entry.edx = result.edx;
             },
             4 => {
                 unsafe {
-                    host_cpuid(
-                        entry.function,
-                        entry.index,
-                        &mut entry.eax as *mut u32,
-                        &mut entry.ebx as *mut u32,
-                        &mut entry.ecx as *mut u32,
-                        &mut entry.edx as *mut u32,
-                    );
+                    let result = __cpuid_count(entry.function, entry.index);
+                    entry.eax = result.eax;
+                    entry.ebx = result.ebx;
+                    entry.ecx = result.ecx;
+                    entry.edx = result.edx;
                 }
                 entry.eax &= !0xFC000000;
             }
@@ -132,34 +114,12 @@ pub fn setup_cpuid(kvm: &kvm::Kvm, vcpu: &kvm::Vcpu, cpu_id: u64, nrcpus: u64) -
 
 /// get host cpu max physical address bits
 pub fn phy_max_address_bits() -> u32 {
-    let mut eax: u32 = 0;
-    let mut ebx: u32 = 0;
-    let mut ecx: u32 = 0;
-    let mut edx: u32 = 0;
     let mut phys_bits: u32 = 36;
 
-    unsafe {
-        host_cpuid(
-            0x80000000,
-            0,
-            &mut eax as *mut u32,
-            &mut ebx as *mut u32,
-            &mut ecx as *mut u32,
-            &mut edx as *mut u32,
-        );
-    }
-    if eax >= 0x80000008 {
-        unsafe {
-            host_cpuid(
-                0x80000008,
-                0,
-                &mut eax as *mut u32,
-                &mut ebx as *mut u32,
-                &mut ecx as *mut u32,
-                &mut edx as *mut u32,
-            );
-        }
-        phys_bits = eax & 0xff;
+    let highest_ext_function = unsafe { __cpuid(0x80000000) };
+    if highest_ext_function.eax >= 0x80000008 {
+        let addr_size = unsafe { __cpuid(0x80000008) };
+        phys_bits = addr_size.eax & 0xff;
     }
 
     phys_bits