linux-kernel - Re: [PATCH v15 02/20] KVM: x86: Add hook for determining max NPT mapping level

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Date: Thu, 2 May 2024 16:11:40 -0700
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Michael Roth <michael.roth@....com>
Cc: kvm@...r.kernel.org, linux-coco@...ts.linux.dev, linux-mm@...ck.org,
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Subject: Re: [PATCH v15 02/20] KVM: x86: Add hook for determining max NPT
 mapping level

On Wed, May 01, 2024 at 03:51:52AM -0500,
Michael Roth <michael.roth@....com> wrote:

..

> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index c6c5018376be..87265b73906a 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1816,6 +1816,7 @@ struct kvm_x86_ops {
>  	void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu);
>  	int (*gmem_prepare)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order);
>  	void (*gmem_invalidate)(kvm_pfn_t start, kvm_pfn_t end);
> +	int (*private_max_mapping_level)(struct kvm *kvm, kvm_pfn_t pfn);

Explicit private prefix is nice.


>  };
>  
>  struct kvm_x86_nested_ops {
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 510eb1117012..0d556da052f6 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4271,6 +4271,20 @@ static inline u8 kvm_max_level_for_order(int order)
>  	return PG_LEVEL_4K;
>  }
>  
> +static u8 kvm_max_private_mapping_level(struct kvm *kvm, kvm_pfn_t pfn,
> +					u8 max_level, int gmem_order)
> +{
> +	if (max_level == PG_LEVEL_4K)
> +		return PG_LEVEL_4K;
> +
> +	max_level = min(kvm_max_level_for_order(gmem_order), max_level);
> +	if (max_level == PG_LEVEL_4K)
> +		return PG_LEVEL_4K;
> +
> +	return min(max_level,
> +		   static_call(kvm_x86_private_max_mapping_level)(kvm, pfn));

If we don't implement this hook, OPTIONAL_RET0 causes always PG_LEVEL_NONE.
Anyway when TDX implements the hook, we can remove OPTIONAL_RET0.

This hook works for TDX by "return PG_LEVEL_4K;".
Reviewed-by: Isaku Yamahata <isaku.yamahata@...el.com>

-- 
Isaku Yamahata <isaku.yamahata@...el.com>