linux-kernel - Re: [PATCH v6 5/7] arm64: kvm: route synchronous external abort exceptions to el2

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Date:   Thu, 07 Sep 2017 17:31:05 +0100
From:   James Morse <james.morse@....com>
To:     Dongjiu Geng <gengdongjiu@...wei.com>
CC:     christoffer.dall@...aro.org, marc.zyngier@....com,
        rkrcmar@...hat.com, linux@...linux.org.uk, catalin.marinas@....com,
        will.deacon@....com, lenb@...nel.org, robert.moore@...el.com,
        lv.zheng@...el.com, mark.rutland@....com, xiexiuqi@...wei.com,
        cov@...eaurora.org, david.daney@...ium.com, suzuki.poulose@....com,
        stefan@...lo-penguin.com, Dave.Martin@....com,
        kristina.martsenko@....com, wangkefeng.wang@...wei.com,
        tbaicar@...eaurora.org, ard.biesheuvel@...aro.org,
        mingo@...nel.org, bp@...e.de, shiju.jose@...wei.com,
        zjzhang@...eaurora.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        devel@...ica.org, mst@...hat.com, john.garry@...wei.com,
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        huangdaode@...ilicon.com, wangzhou1@...ilicon.com,
        huangshaoyu@...wei.com, wuquanming@...wei.com, linuxarm@...wei.com,
        zhengqiang10@...wei.com
Subject: Re: [PATCH v6 5/7] arm64: kvm: route synchronous external abort exceptions
 to el2

Hi Dongjiu Geng,

On 28/08/17 11:38, Dongjiu Geng wrote:
> ARMv8.2 adds a new bit HCR_EL2.TEA which controls to
> route synchronous external aborts to EL2, and adds a
> trap control bit HCR_EL2.TERR which controls to
> trap all Non-secure EL1&0 error record accesses to EL2.
>
> This patch enables the two bits for the guest OS.
> when an synchronous abort is generated in the guest OS,

> it will trap to EL3 firmware, EL3 firmware will check the
> HCR_EL2.TEA value to decide to jump to hypervisor or host
> OS.

(This is what you are using this for, the patch has nothing to do with EL3.)


> Enabling HCR_EL2.TERR makes error record access
> from guest trap to EL2.


KVM already handles external aborts from lower exception levels, no more work
needs doing for TEA.

What happens when a guest access the RAS-Error-Record registers?

Before we can set HCR_EL2.TERR I think we need to add some minimal emulation for
the registers it traps. Most of them should be RAZ/WI, so it should be
straightforward. (I think KVMs default is to emulate an undef for unknown traps).

Eventually we will want to back this with a page of memory that lets
Qemu/kvmtool configure what the guest can see. (i.e. the emulated machine's
errors for kernel-first handling.)


Thanks,

James