Commit 11b41626 authored Jun 18, 2019 by James Morse Committed by Marc Zyngier Jul 05, 2019

KVM: arm64: Skip more of the SError vaxorcism



During __guest_exit() we need to consume any SError left pending by the
guest so it doesn't contaminate the host. With v8.2 we use the
ESB-instruction. For systems without v8.2, we use dsb+isb and unmask
SError. We do this on every guest exit.

Use the same dsb+isr_el1 trick, this lets us know if an SError is pending
after the dsb, allowing us to skip the isb and self-synchronising PSTATE
write if its not.

This means SError remains masked during KVM's world-switch, so any SError
that occurs during this time is reported by the host, instead of causing
a hyp-panic.

As we're benchmarking this code lets polish the layout. If you give gcc
likely()/unlikely() hints in an if() condition, it shuffles the generated
assembly so that the likely case is immediately after the branch. Lets
do the same here.

Signed-off-by: James Morse <james.morse@arm.com>

Changes since v2:
 * Added isb after the dsb to prevent an early read

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

parent dad6321f

arch/arm64/kvm/hyp/entry.S

+10 −4

Original line number	Diff line number	Diff line
		@@ -151,8 +151,16 @@ alternative_if ARM64_HAS_RAS_EXTN
		orr x0, x0, #(1<<ARM_EXIT_WITH_SERROR_BIT)
		1: ret
		alternative_else
		// If we have a pending asynchronous abort, now is the
		// time to find out. From your VAXorcist book, page 666:
		dsb sy // Synchronize against in-flight ld/st
		isb // Prevent an early read of side-effect free ISR
		mrs x2, isr_el1
		tbnz x2, #8, 2f // ISR_EL1.A
		ret
		nop
		2:
		alternative_endif
		// We know we have a pending asynchronous abort, now is the
		// time to flush it out. From your VAXorcist book, page 666:
		// "Threaten me not, oh Evil one! For I speak with
		// the power of DEC, and I command thee to show thyself!"
		mrs x2, elr_el2
		@@ -160,9 +168,7 @@ alternative_else
		mrs x4, spsr_el2
		mov x5, x0

		dsb sy // Synchronize against in-flight ld/st
		msr daifclr, #4 // Unmask aborts
		alternative_endif

		// This is our single instruction exception window. A pending
		// SError is guaranteed to occur at the earliest when we unmask

Admin message