linux-kernel - Re: [PATCH 10/16] KVM: x86/tdp_mmu: Support TDX private mapping for TDP MMU

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Date: Tue, 28 May 2024 19:43:20 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: Isaku Yamahata <isaku.yamahata@...el.com>
Cc: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
	"seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>, 
	"sagis@...gle.com" <sagis@...gle.com>, 
	"isaku.yamahata@...ux.intel.com" <isaku.yamahata@...ux.intel.com>, "Aktas, Erdem" <erdemaktas@...gle.com>, 
	"Zhao, Yan Y" <yan.y.zhao@...el.com>, 
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "dmatlack@...gle.com" <dmatlack@...gle.com>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/16] KVM: x86/tdp_mmu: Support TDX private mapping for
 TDP MMU

On Tue, May 21, 2024 at 1:32 AM Isaku Yamahata <isaku.yamahata@...el.com> wrote:
> +static void vt_adjust_max_pa(void)
> +{
> +       u64 tme_activate;
> +
> +       mmu_max_gfn = __kvm_mmu_max_gfn();
> +       rdmsrl(MSR_IA32_TME_ACTIVATE, tme_activate);
> +       if (!(tme_activate & TME_ACTIVATE_LOCKED) ||
> +           !(tme_activate & TME_ACTIVATE_ENABLED))
> +               return;
> +
> +       mmu_max_gfn -= (gfn_t)TDX_RESERVED_KEYID_BITS(tme_activate);

This would be be >>=, not "-=". But I think this should not look at
TME MSRs directly, instead it can use boot_cpu_data.x86_phys_bits. You
can use it instead of shadow_phys_bits in __kvm_mmu_max_gfn() and then
VMX does not need any adjustment.

That said, this is not a bugfix, it's just an optimization.

Paolo

> +       }
>
>  out:
>         /* kfree() accepts NULL. */
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 7f89405c8bc4..c519bb9c9559 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12693,6 +12693,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>         if (ret)
>                 goto out;
>
> +       kvm->arch.mmu_max_gfn = __kvm_mmu_max_gfn();
>         kvm_mmu_init_vm(kvm);
>
>         ret = static_call(kvm_x86_vm_init)(kvm);
> @@ -13030,7 +13031,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>                 return -EINVAL;
>
>         if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) {
> -               if ((new->base_gfn + new->npages - 1) > kvm_mmu_max_gfn())
> +               if ((new->base_gfn + new->npages - 1) > kvm_mmu_max_gfn(kvm))
>                         return -EINVAL;
>
>  #if 0
>
> --
> Isaku Yamahata <isaku.yamahata@...el.com>
>