linux-kernel - Re: [PATCH] Fixes: f32fb32820b1 ("KVM: x86: Add hook for determining max NPT mapping level")

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Message-ID: <CABgObfZbS7LsKM_w2ZSpb82oBAHF=pJfVJ+45k7=vVVWHK5Y6A@mail.gmail.com>
Date: Thu, 1 Aug 2024 20:15:22 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Ackerley Tng <ackerleytng@...gle.com>
Cc: michael.roth@....com, ak@...ux.intel.com, alpergun@...gle.com, 
	ardb@...nel.org, ashish.kalra@....com, bp@...en8.de, 
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	jarkko@...nel.org, jmattson@...gle.com, vannapurve@...gle.com, 
	erdemaktas@...gle.com, jroedel@...e.de, kirill@...temov.name, 
	kvm@...r.kernel.org, liam.merwick@...cle.com, linux-coco@...ts.linux.dev, 
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, luto@...nel.org, mingo@...hat.com, 
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	thomas.lendacky@....com, tobin@....com, tony.luck@...el.com, vbabka@...e.cz, 
	vkuznets@...hat.com, x86@...nel.org
Subject: Re: [PATCH] Fixes: f32fb32820b1 ("KVM: x86: Add hook for determining
 max NPT mapping level")

On Thu, Aug 1, 2024 at 7:40 PM Ackerley Tng <ackerleytng@...gle.com> wrote:
>
> The `if (req_max_level)` test was meant ignore req_max_level if
> PG_LEVEL_NONE was returned. Hence, this function should return
> max_level instead of the ignored req_max_level.
>
> Signed-off-by: Ackerley Tng <ackerleytng@...gle.com>
> Change-Id: I403898aacc379ed98ba5caa41c9f1c52f277adc2

It's worth pointing out that this is only a latent issue for now,
since guest_memfd does not support large pages ( __kvm_gmem_get_pfn
always returns 0).

Queued with a small note in the commit message and fixed subject.

Thanks,

Paolo


> ---
>  arch/x86/kvm/mmu/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 901be9e420a4..e6b73774645d 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -4335,7 +4335,7 @@ static u8 kvm_max_private_mapping_level(struct kvm *kvm, kvm_pfn_t pfn,
>         if (req_max_level)
>                 max_level = min(max_level, req_max_level);
>
> -       return req_max_level;
> +       return max_level;
>  }
>
>  static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> --
> 2.46.0.rc2.264.g509ed76dc8-goog
>