[Xen-devel] [tip:x86/urgent] x86/microcode/intel: Replace sync_core() with native_cpuid()

[tip-bot for Andy Lutomirski <tipbot@xxxxxxxxx>]

Commit-ID:  484d0e5c7943644cc46e7308a8f9d83be598f2b9
Gitweb:     http://git.kernel.org/tip/484d0e5c7943644cc46e7308a8f9d83be598f2b9
Author:     Andy Lutomirski <luto@xxxxxxxxxx>
AuthorDate: Fri, 9 Dec 2016 10:24:07 -0800
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Mon, 19 Dec 2016 11:54:21 +0100

x86/microcode/intel: Replace sync_core() with native_cpuid()

The Intel microcode driver is using sync_core() to mean "do CPUID
with EAX=1".  I want to rework sync_core(), but first the Intel
microcode driver needs to stop depending on its current behavior.

Reported-by: Henrique de Moraes Holschuh <hmh@xxxxxxxxxx>
Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
Acked-by: Borislav Petkov <bp@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: One Thousand Gnomes <gnomes@xxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Matthew Whitehead <tedheadster@xxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: xen-devel <Xen-devel@xxxxxxxxxxxxx>
Link: 
http://lkml.kernel.org/r/535a025bb91fed1a019c5412b036337ad239e5bb.1481307769.git.luto@xxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

---
 arch/x86/kernel/cpu/microcode/intel.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/microcode/intel.c 
b/arch/x86/kernel/cpu/microcode/intel.c
index 54d50c3..b624b54 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -368,6 +368,26 @@ next:
        return patch;
 }
 
+static void cpuid_1(void)
+{
+       /*
+        * According to the Intel SDM, Volume 3, 9.11.7:
+        *
+        *   CPUID returns a value in a model specific register in
+        *   addition to its usual register return values. The
+        *   semantics of CPUID cause it to deposit an update ID value
+        *   in the 64-bit model-specific register at address 08BH
+        *   (IA32_BIOS_SIGN_ID). If no update is present in the
+        *   processor, the value in the MSR remains unmodified.
+        *
+        * Use native_cpuid -- this code runs very early and we don't
+        * want to mess with paravirt.
+        */
+       unsigned int eax = 1, ebx, ecx = 0, edx;
+
+       native_cpuid(&eax, &ebx, &ecx, &edx);
+}
+
 static int collect_cpu_info_early(struct ucode_cpu_info *uci)
 {
        unsigned int val[2];
@@ -393,7 +413,7 @@ static int collect_cpu_info_early(struct ucode_cpu_info 
*uci)
        native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
        /* As documented in the SDM: Do a CPUID 1 here */
-       sync_core();
+       cpuid_1();
 
        /* get the current revision from MSR 0x8B */
        native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
@@ -593,7 +613,7 @@ static int apply_microcode_early(struct ucode_cpu_info 
*uci, bool early)
        native_wrmsrl(MSR_IA32_UCODE_REV, 0);
 
        /* As documented in the SDM: Do a CPUID 1 here */
-       sync_core();
+       cpuid_1();
 
        /* get the current revision from MSR 0x8B */
        native_rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);
@@ -805,7 +825,7 @@ static int apply_microcode_intel(int cpu)
        wrmsrl(MSR_IA32_UCODE_REV, 0);
 
        /* As documented in the SDM: Do a CPUID 1 here */
-       sync_core();
+       cpuid_1();
 
        /* get the current revision from MSR 0x8B */
        rdmsr(MSR_IA32_UCODE_REV, val[0], val[1]);

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