Re: [PATCH for-4.2 1/2] i386: Add new versions of Skylake/Cascadelake/Icelake without TSX

[Kashyap Chamarthy]

On Wed, Nov 20, 2019 at 01:49:11PM -0300, Eduardo Habkost wrote:
> One of the mitigation methods for TAA[1] is to disable TSX
> support on the host system.  Linux added a mechanism to disable
> TSX globally through the kernel command line, and many Linux
> distributions now default to tsx=off.  This makes existing CPU
> models that have HLE and RTM enabled not usable anymore.
>
> Add new versions of all CPU models that have the HLE and RTM
> features enabled, that can be used when TSX is disabled in the
> host system.
>
> References:
>
> [1] TAA, TSX asynchronous Abort:
>     
> https://software.intel.com/security-software-guidance/insights/deep-dive-intel-transactional-synchronization-extensions-intel-tsx-asynchronous-abort
>     
> https://www.kernel.org/doc/html/latest/admin-guide/hw-vuln/tsx_async_abort.html
>
> Signed-off-by: Eduardo Habkost <address@hidden>
> ---

FWIW:

    Tested-by: Kashyap Chamarthy <address@hidden>

Here are _all_ the Cascadelake/Icelake/Skylake variants I see with your
patches applied:

    $> ./qemu-system-x86_64 -cpu help | egrep  
'(Cascadelake.*|Icelake.*|Skylake.*)'
    x86 Cascadelake-Server    (alias configured by machine type)
    x86 Cascadelake-Server-noTSX  (alias of Cascadelake-Server-v3)
    x86 Cascadelake-Server-v1  Intel Xeon Processor (Cascadelake)
    x86 Cascadelake-Server-v2  Intel Xeon Processor (Cascadelake)
    x86 Cascadelake-Server-v3  Intel Xeon Processor (Cascadelake)
    x86 Icelake-Client        (alias configured by machine type)
    x86 Icelake-Client-noTSX  (alias of Icelake-Client-v2)
    x86 Icelake-Client-v1     Intel Core Processor (Icelake)
    x86 Icelake-Client-v2     Intel Core Processor (Icelake)
    x86 Icelake-Server        (alias configured by machine type)
    x86 Icelake-Server-noTSX  (alias of Icelake-Server-v2)
    x86 Icelake-Server-v1     Intel Xeon Processor (Icelake)
    x86 Icelake-Server-v2     Intel Xeon Processor (Icelake)
    x86 Skylake-Client        (alias configured by machine type)
    x86 Skylake-Client-IBRS   (alias of Skylake-Client-v2)
    x86 Skylake-Client-noTSX-IBRS  (alias of Skylake-Client-v3)
    x86 Skylake-Client-v1     Intel Core Processor (Skylake)
    x86 Skylake-Client-v2     Intel Core Processor (Skylake, IBRS)
    x86 Skylake-Client-v3     Intel Core Processor (Skylake, IBRS)
    x86 Skylake-Server        (alias configured by machine type)
    x86 Skylake-Server-IBRS   (alias of Skylake-Server-v2)
    x86 Skylake-Server-noTSX-IBRS  (alias of Skylake-Server-v3)
    x86 Skylake-Server-v1     Intel Xeon Processor (Skylake)
    x86 Skylake-Server-v2     Intel Xeon Processor (Skylake, IBRS)
    x86 Skylake-Server-v3     Intel Xeon Processor (Skylake, IBRS)


Test with system QEMU
---------------------

Where `cat system-qemu.sh` is:

    #!/usr/bin/env bash
    args=(
     -display none
     -cpu Skylake-Client-IBRS
     -no-user-config
     -machine q35,accel=kvm
     -nodefaults
     -m 2048
     -serial stdio
     -drive file=/export/vm1.qcow2,format=qcow2,if=virtio
    )
    /usr/bin/qemu-system-x86_64 "${args[@]}"

Run it:

    $> ./system-qemu.sh
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.01H:ECX.aes [bit 25]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.hle [bit 4]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.rtm [bit 11]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.rdseed [bit 18]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.adx [bit 19]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.smap [bit 20]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.80000001H:ECX.3dnowprefetch [bit 8]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.0DH:EAX.xsavec [bit 1]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.0DH:EAX.xgetbv1 [bit 2]
    [...]

Notice that it is (correctly) complaining about about "hle" and "rtm".


Test with patched QEMU
----------------------

Now, with a QEMU built with your both patches, and using the -noTSX-IBRS
model:

Where `cat patched-qemu.sh` is:

    #!/usr/bin/env bash
    args=(
     -display none
     -cpu Skylake-Client-noTSX-IBRS
     -no-user-config
     -machine q35,accel=kvm
     -nodefaults
     -m 2048
     -serial stdio
     -drive file=/export/vm1.qcow2,format=qcow2,if=virtio
    )
    ~/build/qemu/x86_64-softmmu/qemu-system-x86_64 "${args[@]}"

Run it:

    $> ./patched-qemu.sh
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.01H:ECX.aes [bit 25]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.rdseed [bit 18]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.adx [bit 19]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.07H:EBX.smap [bit 20]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.80000001H:ECX.3dnowprefetch [bit 8]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.0DH:EAX.xsavec [bit 1]
    qemu-system-x86_64: warning: host doesn't support requested feature: 
CPUID.0DH:EAX.xgetbv1 [bit 2]
    [...]

Here it doesn't complain (also correctly so) about "hle" and "rtm",
because the -noTSX-IBRS model disabled them :-)


>  target/i386/cpu.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
>
> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> index 296b491607..0267e08612 100644
> --- a/target/i386/cpu.c
> +++ b/target/i386/cpu.c
> @@ -2474,6 +2474,14 @@ static X86CPUDefinition builtin_x86_defs[] = {
>                      { /* end of list */ }
>                  }
>              },
> +            {
> +                .version = 3,
> +                .props = (PropValue[]) {
> +                    { "hle", "off" },
> +                    { "rtm", "off" },
> +                    { /* end of list */ }
> +                }
> +            },
>              { /* end of list */ }
>          }
>      },
> @@ -2541,6 +2549,14 @@ static X86CPUDefinition builtin_x86_defs[] = {
>                      { /* end of list */ }
>                  }
>              },
> +            {
> +                .version = 3,
> +                .props = (PropValue[]) {
> +                    { "hle", "off" },
> +                    { "rtm", "off" },
> +                    { /* end of list */ }
> +                }
> +            },
>              { /* end of list */ }
>          }
>      },
> @@ -2608,6 +2624,13 @@ static X86CPUDefinition builtin_x86_defs[] = {
>                    { /* end of list */ }
>                },
>              },
> +            { .version = 3,
> +              .props = (PropValue[]) {
> +                  { "hle", "off" },
> +                  { "rtm", "off" },
> +                  { /* end of list */ }
> +              },
> +            },
>              { /* end of list */ }
>          }
>      },
> @@ -2665,6 +2688,18 @@ static X86CPUDefinition builtin_x86_defs[] = {
>              CPUID_6_EAX_ARAT,
>          .xlevel = 0x80000008,
>          .model_id = "Intel Core Processor (Icelake)",
> +        .versions = (X86CPUVersionDefinition[]) {
> +            { .version = 1 },
> +            {
> +                .version = 2,
> +                .props = (PropValue[]) {
> +                    { "hle", "off" },
> +                    { "rtm", "off" },
> +                    { /* end of list */ }
> +                },
> +            },
> +            { /* end of list */ }
> +        }
>      },
>      {
>          .name = "Icelake-Server",
> @@ -2723,6 +2758,18 @@ static X86CPUDefinition builtin_x86_defs[] = {
>              CPUID_6_EAX_ARAT,
>          .xlevel = 0x80000008,
>          .model_id = "Intel Xeon Processor (Icelake)",
> +        .versions = (X86CPUVersionDefinition[]) {
> +            { .version = 1 },
> +            {
> +                .version = 2,
> +                .props = (PropValue[]) {
> +                    { "hle", "off" },
> +                    { "rtm", "off" },
> +                    { /* end of list */ }
> +                },
> +            },
> +            { /* end of list */ }
> +        }
>      },
>      {
>          .name = "Denverton",
> --
> 2.21.0
>

--
/kashyap