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

2018-12-12 Thread Eduardo Habkost
On Tue, Dec 11, 2018 at 05:14:40PM +0100, Borislav Petkov wrote:
> + qemu-devel.
> 
> On Tue, Dec 11, 2018 at 03:30:17PM +, Daniel P. Berrangé 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 
> 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 
> ---
>  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",\
> +},

This looks correct.

>  
>  #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",\

Why did you remove this entry from PC_COMPAT_2_4?

We must keep compatibility with old behavior of Opteron_G2 on
pc-2.4, even if the old behavior was incorrect.


>  },{\
>  .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 */

This is Opteron_G2, and feature is not being added.  Looks
correct.

>  .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,

This is Opteron_G3.  Looks correct.

>  .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 | 

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

2018-12-11 Thread Borislav Petkov via Qemu-devel
+ qemu-devel.

On Tue, Dec 11, 2018 at 03:30:17PM +, Daniel P. Berrangé 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 
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 
---
 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 |