On Thu, Nov 14, 2019 at 08:07:35PM +1100, Michael Ellerman wrote:

On Thu, 2019-05-02 at 21:09:07 UTC, Gustavo Walbon wrote:

...

From: "Gustavo L. F. Walbon" gwalbon@linux.ibm.com

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 gwalbon@linux.ibm.com Signed-off-by: Mauro S. M. Rodrigues maurosr@linux.vnet.ibm.com

Applied to powerpc next, thanks.

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

cheers

Fixes: ff348355e9c7 ("powerpc/64s: Enhance the information in cpu_show_meltdown()")

Thanks

Michal