[PATCH] target-i386: Reenable RDTSCP support on Opteron_G[345] CPU models

[Borislav Petkov]

+ qemu-devel.

On Tue, Dec 11, 2018 at 03:30:17PM +0000, Daniel P. Berrangà wrote:
> Great, then, this is a non-issue - we just need to mention that fact
> in the commit that sets the min version for the kernel

Ok, here's a first draft ontop of Eduardo's machine-next branch from
http://github.com/ehabkost/qemu

Also, thanks for the help Eduardo! :-)

---
From: Borislav Petkov <bp@xxxxxxx>
Date: Tue, 11 Dec 2018 17:01:00 +0100

The missing functionality was added ~3 years ago with the Linux commit

  46896c73c1a4 ("KVM: svm: add support for RDTSCP")

so reenable RDTSCP support on those CPU models.

Opteron_G2 - being family 15, model 6, doesn't have RDTSCP support
(the real hardware doesn't have it. K8 got RDTSCP support with the NPT
models, i.e., models >= 0x40).

Document the host's minimum required kernel version, while at it.

Signed-off-by: Borislav Petkov <bp@xxxxxxx>
---
 include/hw/i386/pc.h | 17 +++++++++++++----
 qemu-doc.texi        | 13 +++++++++++++
 target/i386/cpu.c    | 11 ++++-------
 3 files changed, 30 insertions(+), 11 deletions(-)

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..16b955cbf985 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 +2814,18 @@ 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.
+
+The OpteronG[345] CPU models require KVM support for RDTSCP, which was
+added with Linux 4.5 which is supported by the major distros. And even
+if RHEL7 has kernel 3.10, KVM there has the required functionality there
+to make it close to a 4.5 or newer kernel.
 
 @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 |
-- 
2.19.1

-- 
Regards/Gruss,
    Boris.

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