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x86/entry/64: Correct the comment over SAVE_AND_SET_GSBASE 

Add the proper explanation why an LFENCE is not needed in the FSGSBASE
case.

Fixes: c82965f9e5 ("x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit")
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200821090710.GE12181@zn.tnic
This commit is contained in:
Borislav Petkov 2020-08-20 11:10:15 +02:00
parent d012a7190f
commit 0b2c605fa4
1 changed files with 3 additions and 2 deletions
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arch/x86/entry/entry_64.S
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@ -840,8 +840,9 @@ SYM_CODE_START_LOCAL(paranoid_entry)
* retrieve and set the current CPUs kernel GSBASE. The stored value
* has to be restored in paranoid_exit unconditionally.
*
* The MSR write ensures that no subsequent load is based on a
* mispredicted GSBASE. No extra FENCE required.
* The unconditional write to GS base below ensures that no subsequent
* loads based on a mispredicted GS base can happen, therefore no LFENCE
* is needed here.
*/
SAVE_AND_SET_GSBASE scratch_reg=%rax save_reg=%rbx
ret