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Message-ID: <878s3c65nr.fsf@vitty.brq.redhat.com>
Date: Mon, 14 Jun 2021 13:34:48 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Vineeth Pillai <viremana@...ux.microsoft.com>,
Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc: "H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"K. Y. Srinivasan" <kys@...rosoft.com>, x86@...nel.org,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hyperv@...r.kernel.org,
Lan Tianyu <Tianyu.Lan@...rosoft.com>,
Michael Kelley <mikelley@...rosoft.com>,
Sean Christopherson <seanjc@...gle.com>,
Tom Lendacky <thomas.lendacky@....com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, Wei Liu <wei.liu@...nel.org>,
Stephen Hemminger <sthemmin@...rosoft.com>,
Haiyang Zhang <haiyangz@...rosoft.com>,
Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH v5 7/7] KVM: SVM: hyper-v: Direct Virtual Flush support
Vineeth Pillai <viremana@...ux.microsoft.com> writes:
> From Hyper-V TLFS:
> "The hypervisor exposes hypercalls (HvFlushVirtualAddressSpace,
> HvFlushVirtualAddressSpaceEx, HvFlushVirtualAddressList, and
> HvFlushVirtualAddressListEx) that allow operating systems to more
> efficiently manage the virtual TLB. The L1 hypervisor can choose to
> allow its guest to use those hypercalls and delegate the responsibility
> to handle them to the L0 hypervisor. This requires the use of a
> partition assist page."
>
> Add the Direct Virtual Flush support for SVM.
>
> Related VMX changes:
> commit 6f6a657c9998 ("KVM/Hyper-V/VMX: Add direct tlb flush support")
>
> Signed-off-by: Vineeth Pillai <viremana@...ux.microsoft.com>
> ---
> arch/x86/kvm/Makefile | 4 ++++
> arch/x86/kvm/svm/svm.c | 2 ++
> arch/x86/kvm/svm/svm_onhyperv.c | 41 +++++++++++++++++++++++++++++++++
> arch/x86/kvm/svm/svm_onhyperv.h | 36 +++++++++++++++++++++++++++++
> 4 files changed, 83 insertions(+)
> create mode 100644 arch/x86/kvm/svm/svm_onhyperv.c
>
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index a06745c2fef1..83331376b779 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -32,6 +32,10 @@ kvm-intel-$(CONFIG_X86_SGX_KVM) += vmx/sgx.o
>
> kvm-amd-y += svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o svm/sev.o
>
> +ifdef CONFIG_HYPERV
> +kvm-amd-y += svm/svm_onhyperv.o
> +endif
> +
> obj-$(CONFIG_KVM) += kvm.o
> obj-$(CONFIG_KVM_INTEL) += kvm-intel.o
> obj-$(CONFIG_KVM_AMD) += kvm-amd.o
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index d2a625411059..5139cb6baadc 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -3779,6 +3779,8 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
> }
> svm->vmcb->save.cr2 = vcpu->arch.cr2;
>
> + svm_hv_update_vp_id(svm->vmcb, vcpu);
> +
> /*
> * Run with all-zero DR6 unless needed, so that we can get the exact cause
> * of a #DB.
> diff --git a/arch/x86/kvm/svm/svm_onhyperv.c b/arch/x86/kvm/svm/svm_onhyperv.c
> new file mode 100644
> index 000000000000..3281856ebd94
> --- /dev/null
> +++ b/arch/x86/kvm/svm/svm_onhyperv.c
> @@ -0,0 +1,41 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * KVM L1 hypervisor optimizations on Hyper-V for SVM.
> + */
> +
> +#include <linux/kvm_host.h>
> +#include "kvm_cache_regs.h"
> +
> +#include <asm/mshyperv.h>
> +
> +#include "svm.h"
> +#include "svm_ops.h"
> +
> +#include "hyperv.h"
> +#include "kvm_onhyperv.h"
> +#include "svm_onhyperv.h"
> +
> +int hv_enable_direct_tlbflush(struct kvm_vcpu *vcpu)
> +{
> + struct hv_enlightenments *hve;
> + struct hv_partition_assist_pg **p_hv_pa_pg =
> + &to_kvm_hv(vcpu->kvm)->hv_pa_pg;
> +
> + if (!*p_hv_pa_pg)
> + *p_hv_pa_pg = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +
> + if (!*p_hv_pa_pg)
> + return -ENOMEM;
> +
> + hve = (struct hv_enlightenments *)to_svm(vcpu)->vmcb->control.reserved_sw;
> +
> + hve->partition_assist_page = __pa(*p_hv_pa_pg);
> + hve->hv_vm_id = (unsigned long)vcpu->kvm;
> + if (!hve->hv_enlightenments_control.nested_flush_hypercall) {
> + hve->hv_enlightenments_control.nested_flush_hypercall = 1;
> + vmcb_mark_dirty(to_svm(vcpu)->vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
> + }
> +
> + return 0;
> +}
> +
> diff --git a/arch/x86/kvm/svm/svm_onhyperv.h b/arch/x86/kvm/svm/svm_onhyperv.h
> index 0f262460b2e6..7487052fcef8 100644
> --- a/arch/x86/kvm/svm/svm_onhyperv.h
> +++ b/arch/x86/kvm/svm/svm_onhyperv.h
> @@ -36,6 +36,8 @@ struct hv_enlightenments {
> */
> #define VMCB_HV_NESTED_ENLIGHTENMENTS VMCB_SW
>
> +int hv_enable_direct_tlbflush(struct kvm_vcpu *vcpu);
> +
> static inline void svm_hv_init_vmcb(struct vmcb *vmcb)
> {
> struct hv_enlightenments *hve =
> @@ -55,6 +57,23 @@ static inline void svm_hv_hardware_setup(void)
> svm_x86_ops.tlb_remote_flush_with_range =
> hv_remote_flush_tlb_with_range;
> }
> +
> + if (ms_hyperv.nested_features & HV_X64_NESTED_DIRECT_FLUSH) {
> + int cpu;
> +
> + pr_info("kvm: Hyper-V Direct TLB Flush enabled\n");
> + for_each_online_cpu(cpu) {
> + struct hv_vp_assist_page *vp_ap =
> + hv_get_vp_assist_page(cpu);
> +
> + if (!vp_ap)
> + continue;
> +
> + vp_ap->nested_control.features.directhypercall = 1;
> + }
> + svm_x86_ops.enable_direct_tlbflush =
> + hv_enable_direct_tlbflush;
> + }
> }
>
> static inline void svm_hv_vmcb_dirty_nested_enlightenments(
> @@ -74,6 +93,18 @@ static inline void svm_hv_vmcb_dirty_nested_enlightenments(
> hve->hv_enlightenments_control.msr_bitmap)
> vmcb_mark_dirty(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
> }
> +
> +static inline void svm_hv_update_vp_id(struct vmcb *vmcb,
> + struct kvm_vcpu *vcpu)
> +{
> + struct hv_enlightenments *hve =
> + (struct hv_enlightenments *)vmcb->control.reserved_sw;
> +
> + if (hve->hv_vp_id != to_hv_vcpu(vcpu)->vp_index) {
> + hve->hv_vp_id = to_hv_vcpu(vcpu)->vp_index;
> + vmcb_mark_dirty(vmcb, VMCB_HV_NESTED_ENLIGHTENMENTS);
> + }
This blows up in testing when no Hyper-V context was created on a vCPU,
e.g. when running KVM selftests (to_hv_vcpu(vcpu) is NULL when no
Hyper-V emulation features were requested on a vCPU but
svm_hv_update_vp_id() is called unconditionally by svm_vcpu_run()).
I'll be sending a patch to fix the immediate issue but I was wondering
why we need to call svm_hv_update_vp_id() from svm_vcpu_run() as VP
index is unlikely to change; we can probably just call it from
kvm_hv_set_msr() instead.
> +}
> #else
>
> static inline void svm_hv_init_vmcb(struct vmcb *vmcb)
> @@ -88,6 +119,11 @@ static inline void svm_hv_vmcb_dirty_nested_enlightenments(
> struct kvm_vcpu *vcpu)
> {
> }
> +
> +static inline void svm_hv_update_vp_id(struct vmcb *vmcb,
> + struct kvm_vcpu *vcpu)
> +{
> +}
> #endif /* CONFIG_HYPERV */
>
> #endif /* __ARCH_X86_KVM_SVM_ONHYPERV_H__ */
--
Vitaly
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