Re: [PATCH 2/3] x86/amd: Enumeration for speculative features/hints

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.08.2021 16:30, Andrew Cooper wrote:
> There is a step change in speculation protections between the Zen1 and Zen2
> microarchitectures.
> 
> Zen1 and older have no special support.  Control bits in non-architectural
> MSRs are used to make lfence be dispatch-serialising (Spectre v1), and to
> disable Memory Disambiguation (Speculative Store Bypass).  IBPB was
> retrofitted in a microcode update, and software methods are required for
> Spectre v2 protections.
> 
> Because the bit controlling Memory Disambiguation is model specific,
> hypervisors are expected to expose a MSR_VIRT_SPEC_CTRL interface which
> abstracts the model specific details.
> 
> Zen2 and later implement the MSR_SPEC_CTRL interface in hardware, and
> virtualise the interface for HVM guests to use.  A number of hint bits are
> specified too to help guide OS software to the most efficient mitigation
> strategy.
> 
> Zen3 introduced a new feature, Predictive Store Forwarding, along with a
> control to disable it in sensitive code.
> 
> Add CPUID and VMCB details for all the new functionality.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
with one suggestion:

> --- a/tools/libs/light/libxl_cpuid.c
> +++ b/tools/libs/light/libxl_cpuid.c
> @@ -274,8 +274,18 @@ int libxl_cpuid_parse_config(libxl_cpuid_policy_list 
> *cpuid, const char* str)
>          {"rstr-fp-err-ptrs", 0x80000008, NA, CPUID_REG_EBX, 2, 1},
>          {"wbnoinvd",     0x80000008, NA, CPUID_REG_EBX,  9,  1},
>          {"ibpb",         0x80000008, NA, CPUID_REG_EBX, 12,  1},
> +        {"ibrs",         0x80000008, NA, CPUID_REG_EBX, 14,  1},
> +        {"amd-stibp",    0x80000008, NA, CPUID_REG_EBX, 15,  1},
> +        {"ibrs-always",  0x80000008, NA, CPUID_REG_EBX, 16,  1},
> +        {"stibp-always", 0x80000008, NA, CPUID_REG_EBX, 17,  1},
> +        {"ibrs-fast",    0x80000008, NA, CPUID_REG_EBX, 18,  1},
> +        {"ibrs-same-mode", 0x80000008, NA, CPUID_REG_EBX, 19,  1},

Here and below, how about dropping the "mode" part of the name?
I can't seem to be able to think of any other "same" that could
possibly apply here.

Jan