Re: [PATCH 3/3] x86/msr: Fix Solaris and turbostat following XSA-351

["Roger Pau Monné" <roger.pau@citrix.com>]

On Tue, Mar 16, 2021 at 04:18:44PM +0000, Andrew Cooper wrote:
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

Thanks!

> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> CC: Wei Liu <wl@xen.org>
> CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> CC: Ian Jackson <iwj@xenproject.org>
> 
> For 4.15 This wants backporting to all security trees, as it is a fix to a
> regression introduced in XSA-351.
> 
> Also it means that users don't need msr_relaxed=1 to unbreak Solaris guests,
> which is a strict useability improvement.
> ---
>  xen/arch/x86/msr.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
> index 5927b6811b..a83a1d7fba 100644
> --- a/xen/arch/x86/msr.c
> +++ b/xen/arch/x86/msr.c
> @@ -188,7 +188,6 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
>      case MSR_TSX_CTRL:
>      case MSR_MCU_OPT_CTRL:
>      case MSR_RTIT_OUTPUT_BASE ... MSR_RTIT_ADDR_B(7):
> -    case MSR_RAPL_POWER_UNIT:
>      case MSR_PKG_POWER_LIMIT  ... MSR_PKG_POWER_INFO:
>      case MSR_DRAM_POWER_LIMIT ... MSR_DRAM_POWER_INFO:
>      case MSR_PP0_POWER_LIMIT  ... MSR_PP0_POLICY:
> @@ -284,6 +283,18 @@ int guest_rdmsr(struct vcpu *v, uint32_t msr, uint64_t *val)
>              goto gp_fault;
>          break;
>  
> +    case MSR_RAPL_POWER_UNIT:
> +        /*
> +         * This MSR is non-architectural.  However, some versions of Solaris
> +         * blindly reads it without a #GP guard, and some versions of
> +         * turbostat crash after expecting a read of /proc/cpu/0/msr not to
> +         * fail.  Read as zero on Intel hardware.
> +         */
> +        if ( !(cp->x86_vendor & X86_VENDOR_INTEL) )
> +            goto gp_fault;

AFAICT from Linux usage this is Intel specific (not present in any of
the clones).

> +        *val = 0;
> +        break;

Do we also need to care about MSR_AMD_RAPL_POWER_UNIT (0xc0010299) for
Solaris?

Thanks, Roger.