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Date: Tue, 6 Feb 2018 13:39:15 +0100
From: Christoffer Dall <christoffer.dall@...aro.org>
To: Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org, arnd@...db.de,
catalin.marinas@....com, cdall@...aro.org,
kvmarm@...ts.cs.columbia.edu, linux-arch@...r.kernel.org,
marc.zyngier@....com, suzuki.poulose@....com, will.deacon@....com,
yao.qi@....com, kernel-hardening@...ts.openwall.com,
linux-kernel@...r.kernel.org, awallis@...eaurora.org
Subject: Re: [PATCHv2 09/12] arm64/kvm: preserve host HCR_EL2 value
On Mon, Nov 27, 2017 at 04:38:03PM +0000, Mark Rutland wrote:
> When restoring HCR_EL2 for the host, KVM uses HCR_HOST_VHE_FLAGS, which
> is a constant value. This works today, as the host HCR_EL2 value is
> always the same, but this will get in the way of supporting extensions
> that require HCR_EL2 bits to be set conditionally for the host.
>
> To allow such features to work without KVM having to explicitly handle
> every possible host feature combination, this patch has KVM save/restore
> the host HCR when switching to/from a guest HCR.
>
> For __{activate,deactivate}_traps(), the HCR save/restore is made common
> across the !VHE and VHE paths. As the host and guest HCR values must
> have E2H set when VHE is in use, register redirection should always be
> in effect at EL2, and this change should not adversely affect the VHE
> code.
>
> For the hyp TLB maintenance code, __tlb_switch_to_host_vhe() is updated
> to toggle the TGE bit with a RMW sequence, as we already do in
> __tlb_switch_to_guest_vhe().
>
> The now unused HCR_HOST_VHE_FLAGS definition is removed.
>
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Reviewed-by: Christoffer Dall <cdall@...aro.org>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: kvmarm@...ts.cs.columbia.edu
> ---
> arch/arm64/include/asm/kvm_arm.h | 1 -
> arch/arm64/include/asm/kvm_host.h | 5 ++++-
> arch/arm64/kvm/hyp/switch.c | 5 +++--
> arch/arm64/kvm/hyp/tlb.c | 6 +++++-
> 4 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 62854d5d1d3b..aa02b05430e8 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -84,7 +84,6 @@
> HCR_AMO | HCR_SWIO | HCR_TIDCP | HCR_RW)
> #define HCR_VIRT_EXCP_MASK (HCR_VSE | HCR_VI | HCR_VF)
> #define HCR_INT_OVERRIDE (HCR_FMO | HCR_IMO)
> -#define HCR_HOST_VHE_FLAGS (HCR_RW | HCR_TGE | HCR_E2H)
>
> /* TCR_EL2 Registers bits */
> #define TCR_EL2_RES1 ((1 << 31) | (1 << 23))
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 674912d7a571..39184aa3e2f2 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -199,10 +199,13 @@ typedef struct kvm_cpu_context kvm_cpu_context_t;
> struct kvm_vcpu_arch {
> struct kvm_cpu_context ctxt;
>
> - /* HYP configuration */
> + /* Guest HYP configuration */
> u64 hcr_el2;
> u32 mdcr_el2;
>
> + /* Host HYP configuration */
> + u64 host_hcr_el2;
> +
> /* Exception Information */
> struct kvm_vcpu_fault_info fault;
>
> diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
> index 525c01f48867..2205f0be3ced 100644
> --- a/arch/arm64/kvm/hyp/switch.c
> +++ b/arch/arm64/kvm/hyp/switch.c
> @@ -71,6 +71,8 @@ static void __hyp_text __activate_traps(struct kvm_vcpu *vcpu)
> {
> u64 val;
>
> + vcpu->arch.host_hcr_el2 = read_sysreg(hcr_el2);
> +
Looking back at this, it seems excessive to switch this at every
round-trip. I think it should be possible to have this as a single
global (or per-CPU) variable that gets restored directly when returning
from the VM.
Thanks,
-Christoffer
> /*
> * We are about to set CPTR_EL2.TFP to trap all floating point
> * register accesses to EL2, however, the ARM ARM clearly states that
> @@ -116,7 +118,6 @@ static void __hyp_text __deactivate_traps_vhe(void)
> MDCR_EL2_TPMS;
>
> write_sysreg(mdcr_el2, mdcr_el2);
> - write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
> write_sysreg(CPACR_EL1_DEFAULT, cpacr_el1);
> write_sysreg(vectors, vbar_el1);
> }
> @@ -129,7 +130,6 @@ static void __hyp_text __deactivate_traps_nvhe(void)
> mdcr_el2 |= MDCR_EL2_E2PB_MASK << MDCR_EL2_E2PB_SHIFT;
>
> write_sysreg(mdcr_el2, mdcr_el2);
> - write_sysreg(HCR_RW, hcr_el2);
> write_sysreg(CPTR_EL2_DEFAULT, cptr_el2);
> }
>
> @@ -151,6 +151,7 @@ static void __hyp_text __deactivate_traps(struct kvm_vcpu *vcpu)
> __deactivate_traps_arch()();
> write_sysreg(0, hstr_el2);
> write_sysreg(0, pmuserenr_el0);
> + write_sysreg(vcpu->arch.host_hcr_el2, hcr_el2);
> }
>
> static void __hyp_text __activate_vm(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/hyp/tlb.c b/arch/arm64/kvm/hyp/tlb.c
> index 73464a96c365..c2b0680efa2c 100644
> --- a/arch/arm64/kvm/hyp/tlb.c
> +++ b/arch/arm64/kvm/hyp/tlb.c
> @@ -49,12 +49,16 @@ static hyp_alternate_select(__tlb_switch_to_guest,
>
> static void __hyp_text __tlb_switch_to_host_vhe(struct kvm *kvm)
> {
> + u64 val;
> +
> /*
> * We're done with the TLB operation, let's restore the host's
> * view of HCR_EL2.
> */
> write_sysreg(0, vttbr_el2);
> - write_sysreg(HCR_HOST_VHE_FLAGS, hcr_el2);
> + val = read_sysreg(hcr_el2);
> + val |= HCR_TGE;
> + write_sysreg(val, hcr_el2);
> }
>
> static void __hyp_text __tlb_switch_to_host_nvhe(struct kvm *kvm)
> --
> 2.11.0
>
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