x86/entry: Optimize local_db_save() for virt

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Because DRn access is 'difficult' with virt; but the DR7 read is cheaper
than a cacheline miss on native, add a virt specific fast path to
local_db_save(), such that when breakpoints are not in use to avoid
touching DRn entirely.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200529213321.187833200@infradead.org

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Peter Zijlstra 2020-05-29 23:27:36 +02:00 • committed by Thomas Gleixner

parent cd840e424f

commit 84b6a34915

3 changed files with 27 additions and 6 deletions

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5

arch/x86/include/asm/debugreg.h

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26

arch/x86/kernel/hw_breakpoint.c

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2

arch/x86/kvm/vmx/nested.c

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