linux-kernel - Re: [PATCH v2 5/6] KVM: x86/mmu: Add helper to convert SPTE value to its shadow page

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Date:   Mon, 25 Jul 2022 16:23:52 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Yosry Ahmed <yosryahmed@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v2 5/6] KVM: x86/mmu: Add helper to convert SPTE value to
 its shadow page

On Sat, Jul 23, 2022 at 01:23:24AM +0000, Sean Christopherson wrote:
> Add a helper to convert a SPTE to its shadow page to deduplicate a
> variety of flows and hopefully avoid future bugs, e.g. if KVM attempts to
> get the shadow page for a SPTE without dropping high bits.
> 
> Opportunistically add a comment in mmu_free_root_page() documenting why
> it treats the root HPA as a SPTE.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
[...]
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -207,6 +207,23 @@ static inline int spte_index(u64 *sptep)
>   */
>  extern u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask;
>  
> +static inline struct kvm_mmu_page *to_shadow_page(hpa_t shadow_page)
> +{
> +	struct page *page = pfn_to_page((shadow_page) >> PAGE_SHIFT);
> +
> +	return (struct kvm_mmu_page *)page_private(page);
> +}
> +
> +static inline struct kvm_mmu_page *spte_to_sp(u64 spte)
> +{
> +	return to_shadow_page(spte & SPTE_BASE_ADDR_MASK);
> +}

spte_to_sp() and sptep_to_sp() are a bit hard to differentiate visually.

Maybe spte_to_child_sp() or to_child_sp()?

> +
> +static inline struct kvm_mmu_page *sptep_to_sp(u64 *sptep)
> +{
> +	return to_shadow_page(__pa(sptep));
> +}
> +
>  static inline bool is_mmio_spte(u64 spte)
>  {
>  	return (spte & shadow_mmio_mask) == shadow_mmio_value &&
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index c163f7cc23ca..d3714200b932 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -5,6 +5,8 @@
>  
>  #include <linux/kvm_host.h>
>  
> +#include "spte.h"
> +
>  hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
>  
>  __must_check static inline bool kvm_tdp_mmu_get_root(struct kvm_mmu_page *root)
> -- 
> 2.37.1.359.gd136c6c3e2-goog
>