x86/process: Allow runtime control of Speculative Store Bypass
The Speculative Store Bypass vulnerability can be mitigated with the Reduced Data Speculation (RDS) feature. To allow finer grained control of this eventually expensive mitigation a per task mitigation control is required. Add a new TIF_RDS flag and put it into the group of TIF flags which are evaluated for mismatch in switch_to(). If these bits differ in the previous and the next task, then the slow path function __switch_to_xtra() is invoked. Implement the TIF_RDS dependent mitigation control in the slow path. If the prctl for controlling Speculative Store Bypass is disabled or no task uses the prctl then there is no overhead in the switch_to() fast path. Update the KVM related speculation control functions to take TID_RDS into account as well. Based on a patch from Tim Chen. Completely rewritten. Signed-off-by:Thomas Gleixner <tglx@linutronix.de> Reviewed-by:
Ingo Molnar <mingo@kernel.org> Reviewed-by:
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent
b617cfc8
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