linux-kernel - Re: [PATCH 5/8] KVM: gmem, x86: Add gmem hook for initializing private memory

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Message-Id: <CUU95GQH9815.1YH1SIFK4O6JG@suppilovahvero>
Date:   Wed, 16 Aug 2023 23:30:16 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     <isaku.yamahata@...el.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Cc:     <isaku.yamahata@...il.com>, "Michael Roth" <michael.roth@....com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Sean Christopherson" <seanjc@...gle.com>, <erdemaktas@...gle.com>,
        "Sagi Shahar" <sagis@...gle.com>,
        "David Matlack" <dmatlack@...gle.com>,
        "Kai Huang" <kai.huang@...el.com>,
        "Zhi Wang" <zhi.wang.linux@...il.com>, <chen.bo@...el.com>,
        <linux-coco@...ts.linux.dev>,
        "Chao Peng" <chao.p.peng@...ux.intel.com>,
        "Ackerley Tng" <ackerleytng@...gle.com>,
        "Vishal Annapurve" <vannapurve@...gle.com>,
        "Yuan Yao" <yuan.yao@...ux.intel.com>,
        "Xu Yilun" <yilun.xu@...el.com>,
        "Quentin Perret" <qperret@...gle.com>, <wei.w.wang@...el.com>,
        "Fuad Tabba" <tabba@...gle.com>
Subject: Re: [PATCH 5/8] KVM: gmem, x86: Add gmem hook for initializing
 private memory

On Tue Aug 15, 2023 at 8:18 PM EEST,  wrote:
> From: Michael Roth <michael.roth@....com>
>
> All gmem pages are expected to be 'private' as defined by a particular
> arch/platform. Platforms like SEV-SNP require additional operations to
> move these pages into a private state, so implement a hook that can be
> used to prepare this memory prior to mapping it into a guest.
>
> In the case of SEV-SNP, whether or not a 2MB page can be mapped via a
> 2MB mapping in the guest's nested page table depends on whether or not
> any subpages within the range have already been initialized as private
> in the RMP table, so this hook will also be used by the KVM MMU to clamp
> the maximum mapping size accordingly.
>
> Signed-off-by: Michael Roth <michael.roth@....com>
> Link: https://lore.kernel.org/r/20230612042559.375660-2-michael.roth@amd.com
>
> ---
> Changes v2 -> v3:
> - Newly added
> ---
>  arch/x86/include/asm/kvm-x86-ops.h |  1 +
>  arch/x86/include/asm/kvm_host.h    |  3 +++
>  arch/x86/kvm/mmu/mmu.c             | 12 ++++++++++--
>  3 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 13bc212cd4bc..439ba4beb5af 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -133,6 +133,7 @@ KVM_X86_OP(msr_filter_changed)
>  KVM_X86_OP(complete_emulated_msr)
>  KVM_X86_OP(vcpu_deliver_sipi_vector)
>  KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
> +KVM_X86_OP_OPTIONAL_RET0(gmem_prepare)
>  
>  #undef KVM_X86_OP
>  #undef KVM_X86_OP_OPTIONAL
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index bbefd79b7950..2bc42f2887fa 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1732,6 +1732,9 @@ struct kvm_x86_ops {
>  	 * Returns vCPU specific APICv inhibit reasons
>  	 */
>  	unsigned long (*vcpu_get_apicv_inhibit_reasons)(struct kvm_vcpu *vcpu);
> +
> +	int (*gmem_prepare)(struct kvm *kvm, struct kvm_memory_slot *slot,
> +			    kvm_pfn_t pfn, gfn_t gfn, u8 *max_level);
>  };
>  
>  struct kvm_x86_nested_ops {
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 05943ccb55a4..06900b01b8f0 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4352,6 +4352,7 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
>  				   struct kvm_page_fault *fault)
>  {
>  	int max_order, r;
> +	u8 max_level;
>  
>  	if (!kvm_slot_can_be_private(fault->slot))
>  		return kvm_do_memory_fault_exit(vcpu, fault);
> @@ -4361,8 +4362,15 @@ static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
>  	if (r)
>  		return r;
>  
> -	fault->max_level = min(kvm_max_level_for_order(max_order),
> -			       fault->max_level);
> +	max_level = kvm_max_level_for_order(max_order);
> +	r = static_call(kvm_x86_gmem_prepare)(vcpu->kvm, fault->slot, fault->pfn,
> +					      fault->gfn, &max_level);
> +	if (r) {
> +		kvm_release_pfn_clean(fault->pfn);
> +		return r;
> +	}
> +
> +	fault->max_level = min(max_level, fault->max_level);
>  	fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY);
>  	return RET_PF_CONTINUE;
>  }
> -- 
> 2.25.1

Acked-by: Jarkko Sakkinen <jarkko@...nel.org>

BR, Jarkko