Hi Robin, On 10/06/2019 17:38, Robin Murphy wrote: > On 10/06/2019 17:30, James Morse wrote: >> 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. >> >> 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. >> 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 > It doesn't appear that anyone cares much about x2 containing the masked value after > returning, so is this just a needlessly long-form TBNZ? Yes, I'd make a third-rate compiler. (I almost certainly had 'cmp x2, xzr' in there at some point!) Thanks, James _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
