Re: kvm: RDTSCP on AMD

[Borislav Petkov <bp@alien8.de>]

On Mon, Dec 10, 2018 at 05:47:25PM -0200, Eduardo Habkost wrote:
> On Mon, Dec 10, 2018 at 07:41:53PM +0100, Borislav Petkov wrote:
> > On Mon, Dec 10, 2018 at 04:37:30PM -0200, Eduardo Habkost wrote:
> > > It isn't as simply as reverting commit 33b5e8c03ae7, but we can
> > > surely re-add RDTSCP on pc-*-4.0 and newer.
> > 
> > Sure. If you could only point me to an example how to add that to
> > pc-*-4.0 and newer, I'll gladly cook up a patch and test it.
> 
> Sorry, I forgot to reply to this part.
> 
> See commit 33b5e8c03ae7 for reference.  The differences will be:
> * Instead of removing RDTSCP from builtin_x86_defs, you'll be adding it.
> * Instead of adding rdtscp=on entries to PC_COMPAT_2_4, you'll
>   be adding rdtscp=off entries to PC_COMPAT_3_1.
> 
> PC_COMPAT_3_1 is added by the patch that creates the 4.0
> machine-types.  You can find it on my machine-next branch at:
> 
>   http://github.com/ehabkost/qemu

Thanks for the patient explanation, diff below ontop of your branch.

It is notable to point out that Opteron_G2 - it being family 0xf, model
6 - should not deal with RDTSCP as it doesn't have it.

Although looking at the docs, they say it does but I *have* a K8 laptop
which I just checked and it *doesn't* have RDTSCP in CPUID. So lemme
clarify that aspect first with folks. :)

---
diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index 9d29c4b1df2a..ebc28e816b04 100644
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -296,6 +296,19 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
 
 #define PC_COMPAT_3_1 \
     HW_COMPAT_3_1 \
+    {\
+        .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G4" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },{\
+        .driver   = "Opteron_G5" "-" TYPE_X86_CPU,\
+        .property = "rdtscp",\
+        .value    = "off",\
+    },
 
 #define PC_COMPAT_3_0 \
     HW_COMPAT_3_0 \
@@ -527,10 +540,6 @@ bool e820_get_entry(int, uint32_t, uint64_t *, uint64_t *);
         .driver   = "qemu32" "-" TYPE_X86_CPU,\
         .property = "popcnt",\
         .value    = "on",\
-    },{\
-        .driver   = "Opteron_G2" "-" TYPE_X86_CPU,\
-        .property = "rdtscp",\
-        .value    = "on",\
     },{\
         .driver   = "Opteron_G3" "-" TYPE_X86_CPU,\
         .property = "rdtscp",\
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
 
+@node System requirements
+@chapter System requirements
+
+@section 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..a7def11b27cd 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.

Good mailing practices for 400: avoid top-posting and trim the reply.