Now that we've taken isr_el1 out of the box, there are a few more places we could use it. 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.mo...@arm.com> --- Tested on A57 with v5.2-rc1, do_hvc from [0] v5.2-rc1 mean:4339 stddev:33 v5.2-rc1+patches1-6 mean:4309 stddev:26 with series 0.69% faster [0] https://git.kernel.org/pub/scm/linux/kernel/git/maz/kvm-ws-tests.git/ arch/arm64/kvm/hyp/entry.S | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S index a5a4254314a1..c2de1a1faaf4 100644 --- a/arch/arm64/kvm/hyp/entry.S +++ b/arch/arm64/kvm/hyp/entry.S @@ -161,18 +161,24 @@ 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 + mrs x2, isr_el1 + and x2, x2, #(1<<8) // ISR_EL1.A + cbnz x2, 2f + ret + +2: + // 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 +alternative_endif mrs x3, esr_el2 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 -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
