linux-kernel - Re: [PATCH v2 11/17] kvm: arm64: Configure VTCR per VM

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Message-ID: <be9e8c47-8366-2d8f-8d8d-b8d2f978107b@arm.com>
Date:   Tue, 3 Apr 2018 15:58:41 +0100
From:   James Morse <james.morse@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        cdall@...nel.org, marc.zyngier@....com, punit.agrawal@....com,
        will.deacon@....com, catalin.marinas@....com, pbonzini@...hat.com,
        rkrcmar@...hat.com, ard.biesheuvel@...aro.org,
        peter.maydell@...aro.org, kristina.martsenko@....com,
        mark.rutland@....com
Subject: Re: [PATCH v2 11/17] kvm: arm64: Configure VTCR per VM

Hi Suzuki,

On 27/03/18 14:15, Suzuki K Poulose wrote:
> We set VTCR_EL2 very early during the stage2 init and don't
> touch it ever. This is fine as we had a fixed IPA size. This
> patch changes the behavior to set the VTCR for a given VM,
> depending on its stage2 table. The common configuration for
> VTCR is still performed during the early init as we have to
> retain the hardware access flag update bits (VTCR_EL2_HA)
> per CPU (as they are only set for the CPUs which are capabile).

(Nit: capable)


> The bits defining the number of levels in the page table (SL0)
> and and the size of the Input address to the translation (T0SZ)
> are programmed for each VM upon entry to the guest.

> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 870f4b1..5ccd3ae 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -164,6 +164,12 @@ static void __hyp_text __deactivate_traps(struct kvm_vcpu *vcpu)
>  static void __hyp_text __activate_vm(struct kvm_vcpu *vcpu)
>  {
>  	struct kvm *kvm = kern_hyp_va(vcpu->kvm);
> +	u64 vtcr = read_sysreg(vtcr_el2);
> +
> +	vtcr &= ~VTCR_EL2_PRIVATE_MASK;
> +	vtcr |= VTCR_EL2_SL0(kvm_stage2_levels(kvm)) |
> +		VTCR_EL2_T0SZ(kvm_phys_shift(kvm));
> +	write_sysreg(vtcr, vtcr_el2);
>  	write_sysreg(kvm->arch.vttbr, vttbr_el2);
>  }

Do we need to set this register for tlb maintenance too?
e.g. tlbi for a 3-level-stage2 vm when a 2-level-stage2 vm's vtcr is loaded...

(The ARM-ARM has 'Any of the bits of VTCR_EL2 are permitted to be cached in a TLB'.)


Thanks,

James