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Message-ID: <CABayD+fF7+sn444rMuE_SNwN-SYSPwJr1mrW3qRYw4H7ryi-aw@mail.gmail.com>
Date: Mon, 5 Apr 2021 13:42:42 -0700
From: Steve Rutherford <srutherford@...gle.com>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Joerg Roedel <joro@...tes.org>,
Borislav Petkov <bp@...e.de>,
Tom Lendacky <thomas.lendacky@....com>,
X86 ML <x86@...nel.org>, KVM list <kvm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Sean Christopherson <seanjc@...gle.com>,
Venu Busireddy <venu.busireddy@...cle.com>,
Brijesh Singh <brijesh.singh@....com>,
Will Deacon <will@...nel.org>, maz@...nel.org,
Quentin Perret <qperret@...gle.com>
Subject: Re: [PATCH v11 08/13] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall
On Mon, Apr 5, 2021 at 7:28 AM Ashish Kalra <Ashish.Kalra@....com> wrote:
>
> From: Ashish Kalra <ashish.kalra@....com>
>
> This hypercall is used by the SEV guest to notify a change in the page
> encryption status to the hypervisor. The hypercall should be invoked
> only when the encryption attribute is changed from encrypted -> decrypted
> and vice versa. By default all guest pages are considered encrypted.
>
> The hypercall exits to userspace to manage the guest shared regions and
> integrate with the userspace VMM's migration code.
>
> The patch integrates and extends DMA_SHARE/UNSHARE hypercall to
> userspace exit functionality (arm64-specific) patch from Marc Zyngier,
> to avoid arch-specific stuff and have a common interface
> from the guest back to the VMM and sharing of the host handling of the
> hypercall to support use case for a guest to share memory with a host.
>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: x86@...nel.org
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
> Documentation/virt/kvm/api.rst | 18 ++++++++
> Documentation/virt/kvm/hypercalls.rst | 15 +++++++
> arch/x86/include/asm/kvm_host.h | 2 +
> arch/x86/kvm/svm/sev.c | 61 +++++++++++++++++++++++++++
> arch/x86/kvm/svm/svm.c | 2 +
> arch/x86/kvm/svm/svm.h | 2 +
> arch/x86/kvm/vmx/vmx.c | 1 +
> arch/x86/kvm/x86.c | 12 ++++++
> include/uapi/linux/kvm.h | 8 ++++
> include/uapi/linux/kvm_para.h | 1 +
> 10 files changed, 122 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 307f2fcf1b02..52bd7e475fd6 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5475,6 +5475,24 @@ Valid values for 'type' are:
> Userspace is expected to place the hypercall result into the appropriate
> field before invoking KVM_RUN again.
>
> +::
> +
> + /* KVM_EXIT_DMA_SHARE / KVM_EXIT_DMA_UNSHARE */
> + struct {
> + __u64 addr;
> + __u64 len;
> + __u64 ret;
> + } dma_sharing;
> +
> +This defines a common interface from the guest back to the KVM to support
> +use case for a guest to share memory with a host.
> +
> +The addr and len fields define the starting address and length of the
> +shared memory region.
> +
> +Userspace is expected to place the hypercall result into the "ret" field
> +before invoking KVM_RUN again.
> +
> ::
>
> /* Fix the size of the union. */
> diff --git a/Documentation/virt/kvm/hypercalls.rst b/Documentation/virt/kvm/hypercalls.rst
> index ed4fddd364ea..7aff0cebab7c 100644
> --- a/Documentation/virt/kvm/hypercalls.rst
> +++ b/Documentation/virt/kvm/hypercalls.rst
> @@ -169,3 +169,18 @@ a0: destination APIC ID
>
> :Usage example: When sending a call-function IPI-many to vCPUs, yield if
> any of the IPI target vCPUs was preempted.
> +
> +
> +8. KVM_HC_PAGE_ENC_STATUS
> +-------------------------
> +:Architecture: x86
> +:Status: active
> +:Purpose: Notify the encryption status changes in guest page table (SEV guest)
> +
> +a0: the guest physical address of the start page
> +a1: the number of pages
> +a2: encryption attribute
> +
> + Where:
> + * 1: Encryption attribute is set
> + * 0: Encryption attribute is cleared
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 3768819693e5..78284ebbbee7 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1352,6 +1352,8 @@ struct kvm_x86_ops {
> int (*complete_emulated_msr)(struct kvm_vcpu *vcpu, int err);
>
> void (*vcpu_deliver_sipi_vector)(struct kvm_vcpu *vcpu, u8 vector);
> + int (*page_enc_status_hc)(struct kvm_vcpu *vcpu, unsigned long gpa,
> + unsigned long sz, unsigned long mode);
> };
>
> struct kvm_x86_nested_ops {
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c9795a22e502..fb3a315e5827 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1544,6 +1544,67 @@ static int sev_receive_finish(struct kvm *kvm, struct kvm_sev_cmd *argp)
> return ret;
> }
>
> +static int sev_complete_userspace_page_enc_status_hc(struct kvm_vcpu *vcpu)
> +{
> + vcpu->run->exit_reason = 0;
I don't believe you need to clear exit_reason: it's universally set on exit.
> + kvm_rax_write(vcpu, vcpu->run->dma_sharing.ret);
> + ++vcpu->stat.hypercalls;
> + return kvm_skip_emulated_instruction(vcpu);
> +}
> +
> +int svm_page_enc_status_hc(struct kvm_vcpu *vcpu, unsigned long gpa,
> + unsigned long npages, unsigned long enc)
> +{
> + kvm_pfn_t pfn_start, pfn_end;
> + struct kvm *kvm = vcpu->kvm;
> + gfn_t gfn_start, gfn_end;
> +
> + if (!sev_guest(kvm))
> + return -EINVAL;
> +
> + if (!npages)
> + return 0;
> +
> + gfn_start = gpa_to_gfn(gpa);
> + gfn_end = gfn_start + npages;
> +
> + /* out of bound access error check */
> + if (gfn_end <= gfn_start)
> + return -EINVAL;
> +
> + /* lets make sure that gpa exist in our memslot */
> + pfn_start = gfn_to_pfn(kvm, gfn_start);
> + pfn_end = gfn_to_pfn(kvm, gfn_end);
> +
> + if (is_error_noslot_pfn(pfn_start) && !is_noslot_pfn(pfn_start)) {
> + /*
> + * Allow guest MMIO range(s) to be added
> + * to the shared pages list.
> + */
> + return -EINVAL;
> + }
> +
> + if (is_error_noslot_pfn(pfn_end) && !is_noslot_pfn(pfn_end)) {
> + /*
> + * Allow guest MMIO range(s) to be added
> + * to the shared pages list.
> + */
> + return -EINVAL;
> + }
> +
> + if (enc)
> + vcpu->run->exit_reason = KVM_EXIT_DMA_UNSHARE;
> + else
> + vcpu->run->exit_reason = KVM_EXIT_DMA_SHARE;
> +
> + vcpu->run->dma_sharing.addr = gfn_start;
> + vcpu->run->dma_sharing.len = npages * PAGE_SIZE;
> + vcpu->arch.complete_userspace_io =
> + sev_complete_userspace_page_enc_status_hc;
> +
> + return 0;
> +}
> +
> int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> {
> struct kvm_sev_cmd sev_cmd;
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 58a45bb139f8..3cbf000beff1 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4620,6 +4620,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> .complete_emulated_msr = svm_complete_emulated_msr,
>
> .vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
> +
> + .page_enc_status_hc = svm_page_enc_status_hc,
> };
>
> static struct kvm_x86_init_ops svm_init_ops __initdata = {
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 39e071fdab0c..9cc16d2c0b8f 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -451,6 +451,8 @@ int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
> bool has_error_code, u32 error_code);
> int nested_svm_exit_special(struct vcpu_svm *svm);
> void sync_nested_vmcb_control(struct vcpu_svm *svm);
> +int svm_page_enc_status_hc(struct kvm_vcpu *vcpu, unsigned long gpa,
> + unsigned long npages, unsigned long enc);
>
> extern struct kvm_x86_nested_ops svm_nested_ops;
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 32cf8287d4a7..2c98a5ed554b 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7748,6 +7748,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
> .can_emulate_instruction = vmx_can_emulate_instruction,
> .apic_init_signal_blocked = vmx_apic_init_signal_blocked,
> .migrate_timers = vmx_migrate_timers,
> + .page_enc_status_hc = NULL,
>
> .msr_filter_changed = vmx_msr_filter_changed,
> .complete_emulated_msr = kvm_complete_insn_gp,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f7d12fca397b..ef5c77d59651 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8273,6 +8273,18 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
> kvm_sched_yield(vcpu->kvm, a0);
> ret = 0;
> break;
> + case KVM_HC_PAGE_ENC_STATUS: {
> + int r;
> +
> + ret = -KVM_ENOSYS;
> + if (kvm_x86_ops.page_enc_status_hc) {
> + r = kvm_x86_ops.page_enc_status_hc(vcpu, a0, a1, a2);
> + if (r >= 0)
> + return r;
> + ret = r;
Style nit: Why not just set ret, and return ret if ret >=0?
This looks good. I just had a few nitpicks.
Reviewed-by: Steve Rutherford <srutherford@...gle.com>
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