linux-kernel - Re: [RFC 06/55] KVM: arm64: Add EL2 execution context for nesting

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Message-ID: <20170703090344.GF4066@cbox>
Date:   Mon, 3 Jul 2017 11:03:44 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Jintack Lim <jintack.lim@...aro.org>
Cc:     Christoffer Dall <christoffer.dall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux@...linux.org.uk, Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, vladimir.murzin@....com,
        Suzuki K Poulose <suzuki.poulose@....com>,
        mark.rutland@....com, james.morse@....com,
        lorenzo.pieralisi@....com, kevin.brodsky@....com,
        wcohen@...hat.com, shankerd@...eaurora.org, geoff@...radead.org,
        Andre Przywara <andre.przywara@....com>,
        Eric Auger <eric.auger@...hat.com>, anna-maria@...utronix.de,
        Shih-Wei Li <shihwei@...columbia.edu>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>,
        kvmarm@...ts.cs.columbia.edu, KVM General <kvm@...r.kernel.org>,
        lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jintack Lim <jintack@...columbia.edu>
Subject: Re: [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@...aro.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@...columbia.edu>
> >> Signed-off-by: Christoffer Dall <christoffer.dall@...aro.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