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x86/bugs: Optimize SPEC_CTRL MSR writes

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commit c779bc1a9002fa474175b80e72b85c9bf628abb0 upstream.

When changing SPEC_CTRL for user control, the WRMSR can be delayed
until return-to-user when KERNEL_IBRS has been enabled.

This avoids an MSR write during context switch.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Zijlstra
2022-06-14 23:15:54 +02:00
committed by Greg Kroah-Hartman
parent 62b4db57ee
commit e03415eeba
3 changed files with 14 additions and 8 deletions
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2
arch/x86/kernel/process.c
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@@ -584,7 +584,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
}
if (updmsr)
write_spec_ctrl_current(msr);
write_spec_ctrl_current(msr, false);
}
static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)