Messages in this thread | | | Subject | Re: [PATCH v3 0/2] MTE support for KVM guest | From | Steven Price <> | Date | Fri, 2 Oct 2020 16:38:11 +0100 |
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On 02/10/2020 15:36, Andrew Jones wrote: > On Fri, Sep 25, 2020 at 10:36:05AM +0100, Steven Price wrote: >> Version 3 of adding MTE support for KVM guests. See the previous (v2) >> posting for background: >> >> https://lore.kernel.org/r/20200904160018.29481-1-steven.price%40arm.com >> >> These patches add support to KVM to enable MTE within a guest. They are >> based on Catalin's v9 MTE user-space support series[1] (currently in >> next). >> >> Changes since v2: >> >> * MTE is no longer a VCPU feature, instead it is a VM cap. >> >> * Being a VM cap means easier probing (check for KVM_CAP_ARM_MTE). >> >> * The cap must be set before any VCPUs are created, preventing any >> shenanigans where MTE is enabled for the guest after memory accesses >> have been performed. >> >> [1] https://lore.kernel.org/r/20200904103029.32083-1-catalin.marinas@arm.com >> >> Steven Price (2): >> arm64: kvm: Save/restore MTE registers >> arm64: kvm: Introduce MTE VCPU feature >> >> arch/arm64/include/asm/kvm_emulate.h | 3 +++ >> arch/arm64/include/asm/kvm_host.h | 7 +++++++ >> arch/arm64/include/asm/sysreg.h | 3 ++- >> arch/arm64/kvm/arm.c | 9 +++++++++ >> arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 14 ++++++++++++++ >> arch/arm64/kvm/mmu.c | 15 +++++++++++++++ >> arch/arm64/kvm/sys_regs.c | 20 +++++++++++++++----- >> include/uapi/linux/kvm.h | 1 + >> 8 files changed, 66 insertions(+), 6 deletions(-) >> >> -- >> 2.20.1 >> >> > > Hi Steven, > > These patches look fine to me, but I'd prefer we have a working > implementation in QEMU before we get too excited about the KVM > bits. kvmtool isn't sufficient since it doesn't support migration > (at least afaik). In the past we've implemented features in KVM > that look fine, but then issues have been discovered when trying > to enable them from QEMU, where we also support migration. This > feature looks like there's risk of issues with the userspace side. > Although these two patches would probably stay the same, even if > userspace requires more support.
I agree kvmtool isn't a great test because it doesn't support migration. The support in this series is just the basic support for MTE in a guest and we'd need to wait for the QEMU implementation before deciding whether we need any extra support (e.g. kernel interfaces for reading/writing tags as discussed before).
However, I don't think there's much danger of the support in this series changing - so extra support can be added when/if it's needed, but I don't think we need to block these series on that - QEMU can just probe for whatever additional support it needs before enabling MTE in a guest. I plan to rebase/repost after -rc1 when the user space support has been merged.
Steve
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