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Message-ID: <a9043bd0-1467-e922-20f3-243db5e30183@redhat.com>
Date: Fri, 15 Apr 2022 15:56:59 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: isaku.yamahata@...el.com, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org
Cc: isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 065/104] KVM: TDX: vcpu_run: save/restore host
state(host kernel gs)
On 3/4/22 20:49, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> On entering/exiting TDX vcpu, Preserved or clobbered CPU state is different
> from VMX case. Add TDX hooks to save/restore host/guest CPU state.
> Save/restore kernel GS base MSR.
>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
> arch/x86/kvm/vmx/main.c | 28 +++++++++++++++++++++++++--
> arch/x86/kvm/vmx/tdx.c | 39 ++++++++++++++++++++++++++++++++++++++
> arch/x86/kvm/vmx/tdx.h | 4 ++++
> arch/x86/kvm/vmx/x86_ops.h | 4 ++++
> 4 files changed, 73 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 2e5a7a72d560..f9d43f2de145 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -89,6 +89,30 @@ static void vt_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
> return vmx_vcpu_reset(vcpu, init_event);
> }
>
> +static void vt_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
> +{
> + /*
> + * All host state is saved/restored across SEAMCALL/SEAMRET, and the
> + * guest state of a TD is obviously off limits. Deferring MSRs and DRs
> + * is pointless because the TDX module needs to load *something* so as
> + * not to expose guest state.
> + */
> + if (is_td_vcpu(vcpu)) {
> + tdx_prepare_switch_to_guest(vcpu);
> + return;
> + }
> +
> + vmx_prepare_switch_to_guest(vcpu);
> +}
> +
> +static void vt_vcpu_put(struct kvm_vcpu *vcpu)
> +{
> + if (is_td_vcpu(vcpu))
> + return tdx_vcpu_put(vcpu);
> +
> + return vmx_vcpu_put(vcpu);
> +}
> +
> static fastpath_t vt_vcpu_run(struct kvm_vcpu *vcpu)
> {
> if (is_td_vcpu(vcpu))
> @@ -174,9 +198,9 @@ struct kvm_x86_ops vt_x86_ops __initdata = {
> .vcpu_free = vt_vcpu_free,
> .vcpu_reset = vt_vcpu_reset,
>
> - .prepare_guest_switch = vmx_prepare_switch_to_guest,
> + .prepare_guest_switch = vt_prepare_switch_to_guest,
> .vcpu_load = vmx_vcpu_load,
> - .vcpu_put = vmx_vcpu_put,
> + .vcpu_put = vt_vcpu_put,
>
> .update_exception_bitmap = vmx_update_exception_bitmap,
> .get_msr_feature = vmx_get_msr_feature,
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index ebe4f9bf19e7..7a288aae03ba 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1,5 +1,6 @@
> // SPDX-License-Identifier: GPL-2.0
> #include <linux/cpu.h>
> +#include <linux/mmu_context.h>
>
> #include <asm/tdx.h>
>
> @@ -407,6 +408,9 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
> vcpu->arch.guest_state_protected =
> !(to_kvm_tdx(vcpu->kvm)->attributes & TDX_TD_ATTRIBUTE_DEBUG);
>
> + tdx->host_state_need_save = true;
> + tdx->host_state_need_restore = false;
> +
> return 0;
>
> free_tdvpx:
> @@ -420,6 +424,39 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu)
> return ret;
> }
>
> +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_tdx *tdx = to_tdx(vcpu);
> +
> + if (!tdx->host_state_need_save)
> + return;
> +
> + if (likely(is_64bit_mm(current->mm)))
> + tdx->msr_host_kernel_gs_base = current->thread.gsbase;
> + else
> + tdx->msr_host_kernel_gs_base = read_msr(MSR_KERNEL_GS_BASE);
> +
> + tdx->host_state_need_save = false;
> +}
> +
> +static void tdx_prepare_switch_to_host(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_tdx *tdx = to_tdx(vcpu);
> +
> + tdx->host_state_need_save = true;
> + if (!tdx->host_state_need_restore)
> + return;
> +
> + wrmsrl(MSR_KERNEL_GS_BASE, tdx->msr_host_kernel_gs_base);
> + tdx->host_state_need_restore = false;
> +}
> +
> +void tdx_vcpu_put(struct kvm_vcpu *vcpu)
> +{
> + vmx_vcpu_pi_put(vcpu);
> + tdx_prepare_switch_to_host(vcpu);
> +}
> +
> void tdx_vcpu_free(struct kvm_vcpu *vcpu)
> {
> struct vcpu_tdx *tdx = to_tdx(vcpu);
> @@ -535,6 +572,8 @@ fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu)
>
> tdx_vcpu_enter_exit(vcpu, tdx);
>
> + tdx->host_state_need_restore = true;
> +
> vcpu->arch.regs_avail &= ~VMX_REGS_LAZY_LOAD_SET;
> trace_kvm_exit(vcpu, KVM_ISA_VMX);
>
> diff --git a/arch/x86/kvm/vmx/tdx.h b/arch/x86/kvm/vmx/tdx.h
> index e950404ce5de..8b1cf9c158e3 100644
> --- a/arch/x86/kvm/vmx/tdx.h
> +++ b/arch/x86/kvm/vmx/tdx.h
> @@ -84,6 +84,10 @@ struct vcpu_tdx {
> union tdx_exit_reason exit_reason;
>
> bool initialized;
> +
> + bool host_state_need_save;
> + bool host_state_need_restore;
> + u64 msr_host_kernel_gs_base;
> };
>
> static inline bool is_td(struct kvm *kvm)
> diff --git a/arch/x86/kvm/vmx/x86_ops.h b/arch/x86/kvm/vmx/x86_ops.h
> index 44404dd25737..8b871c5f52cf 100644
> --- a/arch/x86/kvm/vmx/x86_ops.h
> +++ b/arch/x86/kvm/vmx/x86_ops.h
> @@ -141,6 +141,8 @@ int tdx_vcpu_create(struct kvm_vcpu *vcpu);
> void tdx_vcpu_free(struct kvm_vcpu *vcpu);
> void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event);
> fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu);
> +void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu);
> +void tdx_vcpu_put(struct kvm_vcpu *vcpu);
>
> int tdx_vm_ioctl(struct kvm *kvm, void __user *argp);
> int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp);
> @@ -162,6 +164,8 @@ static inline int tdx_vcpu_create(struct kvm_vcpu *vcpu) { return -EOPNOTSUPP; }
> static inline void tdx_vcpu_free(struct kvm_vcpu *vcpu) {}
> static inline void tdx_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) {}
> static inline fastpath_t tdx_vcpu_run(struct kvm_vcpu *vcpu) { return EXIT_FASTPATH_NONE; }
> +static inline void tdx_prepare_switch_to_guest(struct kvm_vcpu *vcpu) {}
> +static inline void tdx_vcpu_put(struct kvm_vcpu *vcpu) {}
>
> static inline int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) { return -EOPNOTSUPP; }
> static inline int tdx_vcpu_ioctl(struct kvm_vcpu *vcpu, void __user *argp) { return -EOPNOTSUPP; }
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
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