linux-kernel - Re: kvm: RDTSCP on AMD

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Date:   Mon, 10 Dec 2018 20:42:58 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Eduardo Habkost <ehabkost@...hat.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Jörg Rödel <joro@...tes.org>,
        Andre Przywara <andre.przywara@....com>,
        kvm ML <kvm@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: kvm: RDTSCP on AMD

On Mon, Dec 10, 2018 at 05:06:00PM -0200, Eduardo Habkost wrote:
> I mean documenting it.  We already have code that will print
> warnings if a feature isn't available.
> 
> See my previous attempt to document the minimum kernel version
> at <https://www.mail-archive.com/qemu-devel@nongnu.org/msg486559.html>.

Something like this?

I still have no clue how to add RDTSCP on pc-*-4.0 and newer.

Thx.

---
diff --git a/qemu-doc.texi b/qemu-doc.texi
index f7ad1dfe4b69..913b2ef68d54 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -37,6 +37,7 @@
 * QEMU System emulator for non PC targets::
 * QEMU Guest Agent::
 * QEMU User space emulator::
+* System requirements::
 * Implementation notes::
 * Deprecated features::
 * Supported build platforms::
@@ -2813,6 +2814,13 @@ Act as if the host page size was 'pagesize' bytes
 Run the emulation in single step mode.
 @end table
 
+@...e System requirements
+@...pter System requirements
+
+@...tion KVM kernel module
+
+On x86_64 hosts, the default set of CPU features enabled by the KVM accelerator
+require the host to be running Linux v4.5 or newer.
 
 @include qemu-tech.texi
 
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index f81d35e1f914..34bb5b74136d 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -2706,7 +2706,6 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_DE | CPUID_FP87,
         .features[FEAT_1_ECX] =
             CPUID_EXT_CX16 | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
         .features[FEAT_8000_0001_ECX] =
@@ -2730,9 +2729,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
         .features[FEAT_1_ECX] =
             CPUID_EXT_POPCNT | CPUID_EXT_CX16 | CPUID_EXT_MONITOR |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
-            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_LM | CPUID_EXT2_NX | CPUID_EXT2_SYSCALL |
+	    CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_MISALIGNSSE | CPUID_EXT3_SSE4A |
             CPUID_EXT3_ABM | CPUID_EXT3_SVM | CPUID_EXT3_LAHF_LM,
@@ -2757,10 +2756,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_POPCNT | CPUID_EXT_SSE42 | CPUID_EXT_SSE41 |
             CPUID_EXT_CX16 | CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ |
             CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |
@@ -2788,10 +2786,9 @@ static X86CPUDefinition builtin_x86_defs[] = {
             CPUID_EXT_AES | CPUID_EXT_POPCNT | CPUID_EXT_SSE42 |
             CPUID_EXT_SSE41 | CPUID_EXT_CX16 | CPUID_EXT_FMA |
             CPUID_EXT_SSSE3 | CPUID_EXT_PCLMULQDQ | CPUID_EXT_SSE3,
-        /* Missing: CPUID_EXT2_RDTSCP */
         .features[FEAT_8000_0001_EDX] =
             CPUID_EXT2_LM | CPUID_EXT2_PDPE1GB | CPUID_EXT2_NX |
-            CPUID_EXT2_SYSCALL,
+            CPUID_EXT2_SYSCALL | CPUID_EXT2_RDTSCP,
         .features[FEAT_8000_0001_ECX] =
             CPUID_EXT3_TBM | CPUID_EXT3_FMA4 | CPUID_EXT3_XOP |
             CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_MISALIGNSSE |

-- 
Regards/Gruss,
    Boris.

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