linux-kernel - Re: [PATCH v18 041/121] KVM: x86/mmu: Allow per-VM override of the TDP max page level

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Date: Sun, 28 Jan 2024 22:12:13 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
 erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
 Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
 chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
 Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v18 041/121] KVM: x86/mmu: Allow per-VM override of the
 TDP max page level



On 1/23/2024 7:53 AM, isaku.yamahata@...el.com wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
>
> TDX requires special handling to support large private page.  For
> simplicity, only support 4K page for TD guest for now.  Add per-VM maximum
> page level support to support different maximum page sizes for TD guest and
> conventional VMX guest.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Acked-by: Kai Huang <kai.huang@...el.com>
> ---
>   arch/x86/include/asm/kvm_host.h | 1 +
>   arch/x86/kvm/mmu/mmu.c          | 2 ++
>   arch/x86/kvm/mmu/mmu_internal.h | 2 +-
>   3 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 430d7bd7c37c..313519edd79e 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1283,6 +1283,7 @@ struct kvm_arch {
>   	unsigned long n_requested_mmu_pages;
>   	unsigned long n_max_mmu_pages;
>   	unsigned int indirect_shadow_pages;
> +	int tdp_max_page_level;

Although only TDX need special handling for now, and TDX always use TDP,
but it doesn't necessarily to be TDP, right?
When the value is assigned to kvm_page_fault.max_level, it is also used for
non-TDP code path.

>   	u8 mmu_valid_gen;
>   	struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];
>   	struct list_head active_mmu_pages;
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 54d4c8f1ba68..e93bc16a5e9b 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -6307,6 +6307,8 @@ void kvm_mmu_init_vm(struct kvm *kvm)
>   
>   	kvm->arch.split_desc_cache.kmem_cache = pte_list_desc_cache;
>   	kvm->arch.split_desc_cache.gfp_zero = __GFP_ZERO;
> +
> +	kvm->arch.tdp_max_page_level = KVM_MAX_HUGEPAGE_LEVEL;
>   }
>   
>   static void mmu_free_vm_memory_caches(struct kvm *kvm)
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index 0443bfcf5d9c..2b9377442927 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -296,7 +296,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>   		.nx_huge_page_workaround_enabled =
>   			is_nx_huge_page_enabled(vcpu->kvm),
>   
> -		.max_level = KVM_MAX_HUGEPAGE_LEVEL,
> +		.max_level = vcpu->kvm->arch.tdp_max_page_level,
>   		.req_level = PG_LEVEL_4K,
>   		.goal_level = PG_LEVEL_4K,
>   	};