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

From: Eduardo Habkost
Date: Wed Dec 12 2018 - 14:52:40 EST

On Tue, Dec 11, 2018 at 05:14:40PM +0100, Borislav Petkov wrote:
> + qemu-devel.
>
> On Tue, Dec 11, 2018 at 03:30:17PM +0000, 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 <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",\
> + },

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 | 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,

This is Opteron_G4. Looks correct.


> .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,

This is Opteron_G5. Looks correct.

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

--
Eduardo