linux-kernel - Re: [PATCH 08/12] KVM: remove kvm_arch_gmem_prepare

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Message-ID: <20240717214238.7qsws5ppqkdwtzqp@amd.com>
Date: Wed, 17 Jul 2024 16:42:38 -0500
From: Michael Roth <michael.roth@....com>
To: Paolo Bonzini <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, <seanjc@...gle.com>
Subject: Re: [PATCH 08/12] KVM: remove kvm_arch_gmem_prepare_needed()

On Thu, Jul 11, 2024 at 06:27:51PM -0400, Paolo Bonzini wrote:
> It is enough to return 0 if a guest need not do any preparation.
> This is in fact how sev_gmem_prepare() works for non-SNP guests,
> and it extends naturally to Intel hosts: the x86 callback for
> gmem_prepare is optional and returns 0 if not defined.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/x86.c       |  5 -----
>  include/linux/kvm_host.h |  1 -
>  virt/kvm/guest_memfd.c   | 13 +++----------
>  3 files changed, 3 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a1c85591f92c..4f58423c6148 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -13604,11 +13604,6 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
>  EXPORT_SYMBOL_GPL(kvm_arch_no_poll);
>  
>  #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
> -bool kvm_arch_gmem_prepare_needed(struct kvm *kvm)
> -{
> -	return kvm->arch.vm_type == KVM_X86_SNP_VM;
> -}
> -
>  int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order)
>  {
>  	return static_call(kvm_x86_gmem_prepare)(kvm, pfn, gfn, max_order);
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index eb8404e9aa03..f6e11991442d 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2443,7 +2443,6 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm,
>  
>  #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
>  int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, int max_order);
> -bool kvm_arch_gmem_prepare_needed(struct kvm *kvm);
>  #endif
>  
>  /**
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index f4d82719ec19..509360eefea5 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -29,16 +29,9 @@ static int __kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slo
>  				    pgoff_t index, struct folio *folio)
>  {
>  #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
> -	kvm_pfn_t pfn;
> -	gfn_t gfn;
> -	int rc;
> -
> -	if (!kvm_arch_gmem_prepare_needed(kvm))
> -		return 0;
> -
> -	pfn = folio_file_pfn(folio, index);
> -	gfn = slot->base_gfn + index - slot->gmem.pgoff;
> -	rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));
> +	kvm_pfn_t pfn = folio_file_pfn(folio, index);
> +	gfn_t gfn = slot->base_gfn + index - slot->gmem.pgoff;
> +	int rc = kvm_arch_gmem_prepare(kvm, gfn, pfn, folio_order(folio));

Looks like this hunk was meant to be part of a different patch.

Otherwise:

Reviewed-by: Michael Roth <michael.roth@....com>

-Mike

>  	if (rc) {
>  		pr_warn_ratelimited("gmem: Failed to prepare folio for index %lx GFN %llx PFN %llx error %d.\n",
>  				    index, gfn, pfn, rc);
> -- 
> 2.43.0
> 
> 
>