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[Tim Chen <tim.c.chen@linux.intel.com>]

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From: Tim Chen <tim.c.chen@linux.intel.com>
To: speck for Thomas Gleixner <speck@linutronix.de>
Subject: Re: [patch V11 00/16] SSB 0

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On 05/02/2018 02:51 PM, speck for Thomas Gleixner wrote:
> Changes since V10:
> 
>   - Addressed Ingos review feedback
> 
>   - Picked up Reviewed-bys
> 
> Delta patch below. Bundle is coming in separate mail. Git repo branches are
> updated as well. The master branch contains also the fix for the lost IBRS
> issue Tim was seeing.
> 
> If there are no further issues and nitpicks, I'm going to make the
> changes immutable and changes need to go incremental on top.
> 
> Thanks,
> 
> 	tglx
> 
> 

I notice that this code ignores the current process's TIF_RDS setting
in the prctl case:

#define firmware_restrict_branch_speculation_end()                      \
do {                                                                    \
        u64 val = x86_get_default_spec_ctrl();                          \
                                                                        \
        alternative_msr_write(MSR_IA32_SPEC_CTRL, val,                  \
                              X86_FEATURE_USE_IBRS_FW);                 \
        preempt_enable();                                               \
} while (0)

x86_get_default_spec_ctrl will return x86_spec_ctrl_base, which
will result in x86_spec_ctrl_base written to the MSR
in the prctl case for Intel CPU.  That incorrectly ignores current
process's TIF_RDS setting and the RDS bit will not be set.

Instead, the following value should have been written to the MSR
for Intel CPU:
x86_spec_ctrl_base | rds_tif_to_spec_ctrl(current_thread_info()->flags)

Thanks.

Tim