Subject: Re: [PATCH] Fix wrong message when RFI Flush is disable

From: Michael Ellerman <[email-masked]>
Date: Thu, 14 Nov 2019 20:07:35 +1100 (AEDT)

On Thu, 2019-05-02 at 21:09:07 UTC, Gustavo Walbon wrote:
> From: "Gustavo L. F. Walbon" <[email-masked]>
> 
> The issue was showing "Mitigation" message via sysfs whatever the state of
> "RFI Flush", but it should show "Vulnerable" when it is disabled.
> 
> If you have "L1D private" feature enabled and not "RFI Flush" you are
> vulnerable to meltdown attacks.
> 
> "RFI Flush" is the key feature to mitigate the meltdown whatever the
> "L1D private" state.
> 
> SEC_FTR_L1D_THREAD_PRIV is a feature for Power9 only.
> 
> So the message should be as the truth table shows.
> CPU | L1D private | RFI Flush |                   sysfs               |
> ----| ----------- | --------- | ------------------------------------- |
>  P9 |    False    |   False   | Vulnerable
>  P9 |    False    |   True    | Mitigation: RFI Flush
>  P9 |    True     |   False   | Vulnerable: L1D private per thread
>  P9 |    True     |   True    | Mitigation: RFI Flush, L1D private per
>     |             |           | thread
>  P8 |    False    |   False   | Vulnerable
>  P8 |    False    |   True    | Mitigation: RFI Flush
> 
> Output before this fix:
>  # cat /sys/devices/system/cpu/vulnerabilities/meltdown
>  Mitigation: RFI Flush, L1D private per thread
>  # echo 0 > /sys/kernel/debug/powerpc/rfi_flush
>  # cat /sys/devices/system/cpu/vulnerabilities/meltdown
>  Mitigation: L1D private per thread
> 
> Output after fix:
>  # cat /sys/devices/system/cpu/vulnerabilities/meltdown
>  Mitigation: RFI Flush, L1D private per thread
>  # echo 0 > /sys/kernel/debug/powerpc/rfi_flush
>  # cat /sys/devices/system/cpu/vulnerabilities/meltdown
>  Vulnerable: L1D private per thread
> 
> Link: https://github.com/linuxppc/issues/issues/243
> 
> Signed-off-by: Gustavo L. F. Walbon <[email-masked]>
> Signed-off-by: Mauro S. M. Rodrigues <[email-masked]>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/4e706af3cd8e1d0503c25332b30cad33c97ed442

cheers