* [PATCH v3 0/2] KVM: arm64: Skip more of the SError vaxorcism @ 2019-06-18 15:18 James Morse 2019-06-18 15:18 ` [PATCH v3 1/2] KVM: arm64: Re-mask SError after the one instruction window James Morse 2019-06-18 15:18 ` [PATCH v3 2/2] KVM: arm64: Skip more of the SError vaxorcism James Morse 0 siblings, 2 replies; 3+ messages in thread From: James Morse @ 2019-06-18 15:18 UTC (permalink / raw) To: linux-arm-kernel, kvmarm; +Cc: Marc Zyngier In guest_enter we used ISR_EL1 to know if an SError is pending as we really don't want to take it as an exception. We can do the same in guest_exit, which saves toggling bits in pstate. This lets us leave SError masked for the remainder of world-switch without having to toggle pstate twice. Changes since v2: * Added patch 1 of this series to make the 'SError remains masked' behaviour explicit * Added missing isb before the isr_el1 read. James Morse (2): KVM: arm64: Re-mask SError after the one instruction window KVM: arm64: Skip more of the SError vaxorcism arch/arm64/kvm/hyp/entry.S | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm ^ permalink raw reply [flat|nested] 3+ messages in thread
* [PATCH v3 1/2] KVM: arm64: Re-mask SError after the one instruction window 2019-06-18 15:18 [PATCH v3 0/2] KVM: arm64: Skip more of the SError vaxorcism James Morse @ 2019-06-18 15:18 ` James Morse 2019-06-18 15:18 ` [PATCH v3 2/2] KVM: arm64: Skip more of the SError vaxorcism James Morse 1 sibling, 0 replies; 3+ messages in thread From: James Morse @ 2019-06-18 15:18 UTC (permalink / raw) To: linux-arm-kernel, kvmarm; +Cc: Marc Zyngier KVM consumes any SError that were pending during guest exit with a dsb/isb and unmasking SError. It currently leaves SError unmasked for the rest of world-switch. This means any SError that occurs during this part of world-switch will cause a hyp-panic. We'd much prefer it to remain pending until we return to the host. Signed-off-by: James Morse <james.morse@arm.com> --- arch/arm64/kvm/hyp/entry.S | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S index d9a55503fab7..017ec4189a08 100644 --- a/arch/arm64/kvm/hyp/entry.S +++ b/arch/arm64/kvm/hyp/entry.S @@ -186,6 +186,8 @@ abort_guest_exit_start: .global abort_guest_exit_end abort_guest_exit_end: + msr daifset, #4 // Mask aborts + // If the exception took place, restore the EL1 exception // context so that we can report some information. // Merge the exception code with the SError pending bit. -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm ^ permalink raw reply related [flat|nested] 3+ messages in thread
* [PATCH v3 2/2] KVM: arm64: Skip more of the SError vaxorcism 2019-06-18 15:18 [PATCH v3 0/2] KVM: arm64: Skip more of the SError vaxorcism James Morse 2019-06-18 15:18 ` [PATCH v3 1/2] KVM: arm64: Re-mask SError after the one instruction window James Morse @ 2019-06-18 15:18 ` James Morse 1 sibling, 0 replies; 3+ messages in thread From: James Morse @ 2019-06-18 15:18 UTC (permalink / raw) To: linux-arm-kernel, kvmarm; +Cc: Marc Zyngier 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 --- 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 017ec4189a08..269e7b2da1fd 100644 --- a/arch/arm64/kvm/hyp/entry.S +++ b/arch/arm64/kvm/hyp/entry.S @@ -162,8 +162,16 @@ 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 @@ -171,9 +179,7 @@ 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 -- 2.20.1 _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm ^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-06-18 15:18 UTC | newest] Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-06-18 15:18 [PATCH v3 0/2] KVM: arm64: Skip more of the SError vaxorcism James Morse 2019-06-18 15:18 ` [PATCH v3 1/2] KVM: arm64: Re-mask SError after the one instruction window James Morse 2019-06-18 15:18 ` [PATCH v3 2/2] KVM: arm64: Skip more of the SError vaxorcism James Morse
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