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SubjectRe: [RFC 06/55] KVM: arm64: Add EL2 execution context for nesting
On Mon, Jun 26, 2017 at 10:33:23AM -0400, Jintack Lim wrote:
> Hi Christoffer,
>
> On Wed, Feb 22, 2017 at 6:10 AM, Christoffer Dall <cdall@linaro.org> wrote:
> > On Mon, Jan 09, 2017 at 01:24:02AM -0500, Jintack Lim wrote:
> >> With the nested virtualization support, the context of the guest
> >> includes EL2 register states. The host manages a set of virtual EL2
> >> registers. In addition to that, the guest hypervisor supposed to run in
> >> EL2 is now deprivilaged and runs in EL1. So, the host also manages a set
> >> of shadow system registers to be able to run the guest hypervisor in
> >> EL1.
> >>
> >> Signed-off-by: Jintack Lim <jintack@cs.columbia.edu>
> >> Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>
> >> ---
> >> arch/arm64/include/asm/kvm_host.h | 54 +++++++++++++++++++++++++++++++++++++++
> >> 1 file changed, 54 insertions(+)
> >>
> >> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> >> index c0c8b02..ed78d73 100644
> >> --- a/arch/arm64/include/asm/kvm_host.h
> >> +++ b/arch/arm64/include/asm/kvm_host.h
> >> @@ -146,6 +146,42 @@ enum vcpu_sysreg {
> >> NR_SYS_REGS /* Nothing after this line! */
> >> };
> >>
> >> +enum el2_regs {
> >> + ELR_EL2,
> >> + SPSR_EL2,
> >> + SP_EL2,
> >> + AMAIR_EL2,
> >> + MAIR_EL2,
> >> + TCR_EL2,
> >> + TTBR0_EL2,
> >> + VTCR_EL2,
> >> + VTTBR_EL2,
> >> + VMPIDR_EL2,
> >> + VPIDR_EL2, /* 10 */
> >> + MDCR_EL2,
> >> + CNTHCTL_EL2,
> >> + CNTHP_CTL_EL2,
> >> + CNTHP_CVAL_EL2,
> >> + CNTHP_TVAL_EL2,
> >> + CNTVOFF_EL2,
> >> + ACTLR_EL2,
> >> + AFSR0_EL2,
> >> + AFSR1_EL2,
> >> + CPTR_EL2, /* 20 */
> >> + ESR_EL2,
> >> + FAR_EL2,
> >> + HACR_EL2,
> >> + HCR_EL2,
> >> + HPFAR_EL2,
> >> + HSTR_EL2,
> >> + RMR_EL2,
> >> + RVBAR_EL2,
> >> + SCTLR_EL2,
> >> + TPIDR_EL2, /* 30 */
> >> + VBAR_EL2,
> >> + NR_EL2_REGS /* Nothing after this line! */
> >> +};
> >
> > Why do we have a separate enum and array for the EL2 regs and not simply
> > expand vcpu_sysreg ?
>
> We can expand vcpu_sysreg for the EL2 system registers. For SP_EL2,
> SPSR_EL2, and ELR_EL2, where is the good place to locate them?.
> SP_EL1, SPSR_EL1, and ELR_EL1 registers are saved in the kvm_regs
> structure instead of sysregs[], so I wonder it's better to put them in
> kvm_regs, too.
>
> BTW, what's the reason that those EL1 registers are in kvm_regs
> instead of sysregs[] in the first place?
>

This has mostly to do with the way we export things to userspace, and
for historical reasons.

So we should either expand kvm_regs with the non-sysregs EL2 registers
and expand sys_regs with the EL2 sysregs, or we should put everything
EL2 into an EL2 array. I feel like the first solution will fit more
nicely into the current design, but I don't have a very strong
preference.

You should look at the KVM_{GET,SET}_ONE_REG API definition and think
about how your choice will fit with this.

Marc, any preference?

Thanks,
-Christoffer

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