Re: [PATCH 16/59] KVM: arm64: nv: Save/Restore vEL2 sysregs

Julien Thierry
2019-06-25T08:49:00Z

On 06/21/2019 10:38 AM, Marc Zyngier wrote:
> From: Andre Przywara <andre.przywara@arm.com>
>
> Whenever we need to restore the guest's system registers to the CPU, we
> now need to take care of the EL2 system registers as well. Most of them
> are accessed via traps only, but some have an immediate effect and also
> a guest running in VHE mode would expect them to be accessible via their
> EL1 encoding, which we do not trap.
>
> Split the current __sysreg_{save,restore}_el1_state() functions into
> handling common sysregs, then differentiate between the guest running in
> vEL2 and vEL1.
>
> For vEL2 we write the virtual EL2 registers with an identical format directly
> into their EL1 counterpart, and translate the few registers that have a
> different format for the same effect on the execution when running a
> non-VHE guest guest hypervisor.
>
> [ Commit message reworked and many bug fixes applied by Marc Zyngier
> and Christoffer Dall. ]
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
> ---
> arch/arm64/kvm/hyp/sysreg-sr.c | 160 +++++++++++++++++++++++++++++++--
> 1 file changed, 153 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
> index 62866a68e852..2abb9c3ff24f 100644
> --- a/arch/arm64/kvm/hyp/sysreg-sr.c
> +++ b/arch/arm64/kvm/hyp/sysreg-sr.c

[...]

> @@ -124,10 +167,91 @@ static void __hyp_text __sysreg_restore_user_state(struct kvm_cpu_context *ctxt)
> write_sysreg(ctxt->sys_regs[TPIDRRO_EL0], tpidrro_el0);
> }
>
> -static void __hyp_text __sysreg_restore_el1_state(struct kvm_cpu_context *ctxt)
> +static void __sysreg_restore_vel2_state(struct kvm_cpu_context *ctxt)
> {
> + u64 val;
> +
> + write_sysreg(read_cpuid_id(), vpidr_el2);
> write_sysreg(ctxt->sys_regs[MPIDR_EL1], vmpidr_el2);
> - write_sysreg(ctxt->sys_regs[CSSELR_EL1], csselr_el1);
> + write_sysreg_el1(ctxt->sys_regs[MAIR_EL2], SYS_MAIR);
> + write_sysreg_el1(ctxt->sys_regs[VBAR_EL2], SYS_VBAR);
> + write_sysreg_el1(ctxt->sys_regs[CONTEXTIDR_EL2],SYS_CONTEXTIDR);
> + write_sysreg_el1(ctxt->sys_regs[AMAIR_EL2], SYS_AMAIR);
> +
> + if (__vcpu_el2_e2h_is_set(ctxt)) {
> + /*
> + * In VHE mode those registers are compatible between
> + * EL1 and EL2.
> + */
> + write_sysreg_el1(ctxt->sys_regs[SCTLR_EL2], SYS_SCTLR);
> + write_sysreg_el1(ctxt->sys_regs[CPTR_EL2], SYS_CPACR);
> + write_sysreg_el1(ctxt->sys_regs[TTBR0_EL2], SYS_TTBR0);
> + write_sysreg_el1(ctxt->sys_regs[TTBR1_EL2], SYS_TTBR1);
> + write_sysreg_el1(ctxt->sys_regs[TCR_EL2], SYS_TCR);
> + write_sysreg_el1(ctxt->sys_regs[CNTHCTL_EL2], SYS_CNTKCTL);
> + } else {
> + write_sysreg_el1(translate_sctlr(ctxt->sys_regs[SCTLR_EL2]),
> + SYS_SCTLR);
> + write_sysreg_el1(translate_cptr(ctxt->sys_regs[CPTR_EL2]),
> + SYS_CPACR);
> + write_sysreg_el1(translate_ttbr0(ctxt->sys_regs[TTBR0_EL2]),
> + SYS_TTBR0);
> + write_sysreg_el1(translate_tcr(ctxt->sys_regs[TCR_EL2]),
> + SYS_TCR);
> + write_sysreg_el1(translate_cnthctl(ctxt->sys_regs[CNTHCTL_EL2]),
> + SYS_CNTKCTL);
> + }
> +
> + /*
> + * These registers can be modified behind our back by a fault
> + * taken inside vEL2. Save them, always.
> + */
> + write_sysreg_el1(ctxt->sys_regs[ESR_EL2], SYS_ESR);
> + write_sysreg_el1(ctxt->sys_regs[AFSR0_EL2], SYS_AFSR0);
> + write_sysreg_el1(ctxt->sys_regs[AFSR1_EL2], SYS_AFSR1);
> + write_sysreg_el1(ctxt->sys_regs[FAR_EL2], SYS_FAR);
> + write_sysreg(ctxt->sys_regs[SP_EL2], sp_el1);
> + write_sysreg_el1(ctxt->sys_regs[ELR_EL2], SYS_ELR);
> +
> + val = __fixup_spsr_el2_write(ctxt, ctxt->sys_regs[SPSR_EL2]);
> + write_sysreg_el1(val, SYS_SPSR);
> +}
> +
> +static void __hyp_text __sysreg_restore_vel1_state(struct kvm_cpu_context *ctxt)
> +{
> + u64 mpidr;
> +
> + if (has_vhe()) {
> + struct kvm_vcpu *vcpu;
> +
> + /*
> + * Warning: this hack only works on VHE, because we only
> + * call this with the *guest* context, which is part of
> + * struct kvm_vcpu. On a host context, you'd get pure junk.
> + */
> + vcpu = container_of(ctxt, struct kvm_vcpu, arch.ctxt);

This seems very fragile, just to find out whether the guest has hyp
capabilities. It would be at least nice to make sure this is indeed a
guest context.

The *clean* way to do it could be to have a pointer to kvm_vcpu in the
kvm_cpu_context which would be NULL for host contexts.

Otherwise, I'm under the impression that for a host context,
ctxt->sys_reg[HCR_EL2] == 0 and that this would also be true for a guest
without nested virt capability. Could we use something like that here?

Cheers,

Julien