linux-kernel - Re: [RFC 18/33] KVM: x86: Decouple kvm_get_memory_attributes() from struct kvm's mem_attr

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Message-ID: <24f037ee4547a1726e358900a63755f5db0e6f39.camel@redhat.com>
Date:   Tue, 28 Nov 2023 09:41:46 +0200
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Nicolas Saenz Julienne <nsaenz@...zon.com>, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-hyperv@...r.kernel.org,
        pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        anelkz@...zon.com, graf@...zon.com, dwmw@...zon.co.uk,
        jgowans@...zon.com, corbert@....net, kys@...rosoft.com,
        haiyangz@...rosoft.com, decui@...rosoft.com, x86@...nel.org,
        linux-doc@...r.kernel.org
Subject: Re: [RFC 18/33] KVM: x86: Decouple kvm_get_memory_attributes() from
 struct kvm's mem_attr_array

On Wed, 2023-11-08 at 11:17 +0000, Nicolas Saenz Julienne wrote:
> Decouple kvm_get_memory_attributes() from struct kvm's mem_attr_array to
> allow other memory attribute sources to use the function.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
> ---
>  arch/x86/kvm/mmu/mmu.c   | 5 +++--
>  include/linux/kvm_host.h | 8 +++++---
>  2 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a1fbb905258b..96421234ca88 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -7301,7 +7301,7 @@ static bool hugepage_has_attrs(struct kvm *kvm, struct kvm_memory_slot *slot,
>  
>  	for (gfn = start; gfn < end; gfn += KVM_PAGES_PER_HPAGE(level - 1)) {
>  		if (hugepage_test_mixed(slot, gfn, level - 1) ||
> -		    attrs != kvm_get_memory_attributes(kvm, gfn))
> +		    attrs != kvm_get_memory_attributes(&kvm->mem_attr_array, gfn))
>  			return false;
>  	}
>  	return true;
> @@ -7401,7 +7401,8 @@ void kvm_mmu_init_memslot_memory_attributes(struct kvm *kvm,
>  		 * be manually checked as the attributes may already be mixed.
>  		 */
>  		for (gfn = start; gfn < end; gfn += nr_pages) {
> -			unsigned long attrs = kvm_get_memory_attributes(kvm, gfn);
> +			unsigned long attrs =
> +				kvm_get_memory_attributes(&kvm->mem_attr_array, gfn);
>  
>  			if (hugepage_has_attrs(kvm, slot, gfn, level, attrs))
>  				hugepage_clear_mixed(slot, gfn, level);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 631fd532c97a..4242588e3dfb 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2385,9 +2385,10 @@ static inline void kvm_prepare_memory_fault_exit(struct kvm_vcpu *vcpu,
>  }
>  
>  #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> -static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
> +static inline unsigned long
> +kvm_get_memory_attributes(struct xarray *mem_attr_array, gfn_t gfn)
>  {
> -	return xa_to_value(xa_load(&kvm->mem_attr_array, gfn));
> +	return xa_to_value(xa_load(mem_attr_array, gfn));
>  }

Can we wrap the 'struct xarray *' with a struct even if it will have a single member
to make it clearer what type the 'kvm_get_memory_attributes' receives.
Also maybe rename this to something like 'kvm_get_memory_attributes_for_gfn'?

>  
>  bool kvm_range_has_memory_attributes(struct kvm *kvm, gfn_t start, gfn_t end,
> @@ -2400,7 +2401,8 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
>  static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
>  {
>  	return IS_ENABLED(CONFIG_KVM_PRIVATE_MEM) &&
> -	       kvm_get_memory_attributes(kvm, gfn) & KVM_MEMORY_ATTRIBUTE_PRIVATE;
> +	       kvm_get_memory_attributes(&kvm->mem_attr_array, gfn) &
> +		       KVM_MEMORY_ATTRIBUTE_PRIVATE;
>  }
>  #else
>  static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)


Also if we go with VM per VTL approach, we won't need this, each VM can already have its own memory attributes.

Best regards,
	Maxim Levitsky