Re: [PATCH v2 6/8] KVM: arm64: Add sys_reg_descs for remaining MTE CMO instructions

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] KVM: arm64: possible missing MTE_CMO_INSN entries for DC GVA and
  DC GZVA
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commit c80fdbddf913183cac8f63dfc60ce6f48445eafa
Author: Oliver Upton <oupton@kernel.org>

KVM: arm64: Add sys_reg_descs for remaining MTE CMO instructions

This commit adds MTE_CMO_INSN descriptors with mte_visibility to
sys_insn_descs[] for MTE cache maintenance instructions trapped by
HCR_EL2.TPCP so that they inject an UNDEFINED exception when MTE is not
enabled for the VM.

> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index b456354713443..7f7a197a9ad6b 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
[ ... ]
> @@ -4394,6 +4403,15 @@ static struct sys_reg_desc sys_insn_descs[] = {
>  	SYS_INSN(TLBI_VALE1NXS, handle_tlbi_el1),
>  	SYS_INSN(TLBI_VAALE1NXS, handle_tlbi_el1),
>  
> +	MTE_CMO_INSN(DC_CGVAC, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CGDVAC, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CGVAP, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CGDVAP, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CGVADP, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CGDVADP, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CIGVAC, bad_cmo_trap),
> +	MTE_CMO_INSN(DC_CIGDVAC, bad_cmo_trap),

[Severity: Low]
This question rests on an architecture detail that could not be confirmed
from the kernel source: can SYS_DC_GVA and SYS_DC_GZVA trap to EL2 via
HCR_EL2.TDZ or HFGITR_EL2.DCZVA when MTE is not enabled for the VM?

If so, encoding_to_cgt[] maps both instructions to CGT_HCR_TDZ and
encoding_to_fgt[] maps them to HFGITR_EL2.DCZVA, which is marked NEVER_FGU
in config.c because the trap bit is shared with SYS_DC_ZVA.  Without
MTE_CMO_INSN entries for SYS_DC_GVA and SYS_DC_GZVA in sys_insn_descs[],
triage_sysreg_trap() has neither an FGU bit nor a visibility() callback to
filter them, and will forward traps from a nested guest to L1 when L1 sets
HCR_EL2.TDZ or HFGITR_EL2.DCZVA instead of injecting an UNDEFINED
exception.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261106183154.3590825-1-oupton@kernel.org?part=6