Re: [PATCH v5 7/7] KVM: guest_memfd: Rework PREPARE config and hook into a more generic CONVERT

From: Fuad Tabba

Date: Wed Jul 15 2026 - 05:54:58 EST

On Wed, 15 Jul 2026 at 00:10, Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Rework guest_memfd's "prepare" hook into a more generic "convert" flow in
> anticipation of supporting in-place conversion, at which point KVM will use
> the hook for both to-private and to-shared conversions, not just to
> "prepare" PRIVATE memory.
>
> Opportunistically rename kvm_gmem_prepare_folio() to kvm_gmem_make_private()
> to better reflect its role.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Fuad Tabba <fuad.tabba@xxxxxxxxx>

Cheers,
/fuad

> ---
> arch/x86/include/asm/kvm-x86-ops.h | 2 +-
> arch/x86/include/asm/kvm_host.h | 2 +-
> arch/x86/kvm/Kconfig | 2 +-
> arch/x86/kvm/x86.c | 8 ++++----
> include/linux/kvm_host.h | 6 +++---
> virt/kvm/Kconfig | 2 +-
> virt/kvm/guest_memfd.c | 12 ++++++------
> 7 files changed, 17 insertions(+), 17 deletions(-)
>
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index 76ce691de2f8..1764bad03b17 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -146,7 +146,7 @@ KVM_X86_OP(vcpu_deliver_sipi_vector)
> KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons);
> KVM_X86_OP_OPTIONAL(get_untagged_addr)
> KVM_X86_OP_OPTIONAL(alloc_apic_backing_page)
> -#if defined(CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE) || defined(CONFIG_HAVE_KVM_ARCH_GMEM_RECLAIM)
> +#if defined(CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT) || defined(CONFIG_HAVE_KVM_ARCH_GMEM_RECLAIM)
> KVM_X86_OP_OPTIONAL_RET0(gmem_convert)
> #endif
> #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index f60fec14c61a..08c4af487fa1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1724,7 +1724,7 @@ struct kvm_x86_ops {
>
> gva_t (*get_untagged_addr)(struct kvm_vcpu *vcpu, gva_t gva, unsigned int flags);
> void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu);
> -#if defined(CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE) || defined(CONFIG_HAVE_KVM_ARCH_GMEM_RECLAIM)
> +#if defined(CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT) || defined(CONFIG_HAVE_KVM_ARCH_GMEM_RECLAIM)
> int (*gmem_convert)(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> kvm_pfn_t nr_pages, int max_order, bool to_private);
> #endif
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index e0e7ad015839..538ed1e80332 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -160,7 +160,7 @@ config KVM_AMD_SEV
> depends on CRYPTO_DEV_SP_PSP && !(KVM_AMD=y && CRYPTO_DEV_CCP_DD=m)
> select ARCH_HAS_CC_PLATFORM
> select KVM_GENERIC_MEMORY_ATTRIBUTES
> - select HAVE_KVM_ARCH_GMEM_PREPARE
> + select HAVE_KVM_ARCH_GMEM_CONVERT
> select HAVE_KVM_ARCH_GMEM_RECLAIM
> select HAVE_KVM_ARCH_GMEM_INVALIDATE
> select HAVE_KVM_ARCH_GMEM_POPULATE
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e509d50c247c..11017f49b94a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10619,11 +10619,11 @@ bool kvm_arch_supports_gmem_init_shared(struct kvm *kvm)
> return !kvm_arch_has_private_mem(kvm);
> }
>
> -#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
> -int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> - kvm_pfn_t nr_pages, int max_order)
> +#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
> +int kvm_arch_gmem_convert(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> + kvm_pfn_t nr_pages, int max_order, bool to_private)
> {
> - return kvm_x86_call(gmem_convert)(kvm, gfn, pfn, nr_pages, max_order, true);
> + return kvm_x86_call(gmem_convert)(kvm, gfn, pfn, nr_pages, max_order, to_private);
> }
> #endif
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 0a06234a8a8b..fdbd697d0337 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -2579,9 +2579,9 @@ static inline int kvm_gmem_get_pfn(struct kvm *kvm,
> }
> #endif /* CONFIG_KVM_GUEST_MEMFD */
>
> -#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
> -int kvm_arch_gmem_prepare(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> - kvm_pfn_t nr_pages, int max_order);
> +#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
> +int kvm_arch_gmem_convert(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> + kvm_pfn_t nr_pages, int max_order, bool to_private);
> #endif
>
> #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
> index 617876993225..c3c0ee253fc7 100644
> --- a/virt/kvm/Kconfig
> +++ b/virt/kvm/Kconfig
> @@ -107,7 +107,7 @@ config KVM_GUEST_MEMFD
> select XARRAY_MULTI
> bool
>
> -config HAVE_KVM_ARCH_GMEM_PREPARE
> +config HAVE_KVM_ARCH_GMEM_CONVERT
> bool
> depends on KVM_GUEST_MEMFD
>
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 0f6745f3b919..173a7ed008d1 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -66,10 +66,10 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
> * On successful return the guest sees a zero page so as to avoid
> * leaking host data and the up-to-date flag is set.
> */
> -static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
> - gfn_t gfn, struct folio *folio)
> +static int kvm_gmem_make_private(struct kvm *kvm, struct kvm_memory_slot *slot,
> + gfn_t gfn, struct folio *folio)
> {
> -#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_PREPARE
> +#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_CONVERT
> unsigned long nr_pages = folio_nr_pages(folio);
> pgoff_t index;
>
> @@ -90,8 +90,8 @@ static int kvm_gmem_prepare_folio(struct kvm *kvm, struct kvm_memory_slot *slot,
> gfn = ALIGN_DOWN(gfn, nr_pages);
> index = kvm_gmem_get_index(slot, gfn);
>
> - return kvm_arch_gmem_prepare(kvm, gfn, folio_file_pfn(folio, index),
> - nr_pages, folio_order(folio));
> + return kvm_arch_gmem_convert(kvm, gfn, folio_file_pfn(folio, index),
> + nr_pages, folio_order(folio), true);
> #else
> return 0;
> #endif
> @@ -798,7 +798,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
> folio_mark_uptodate(folio);
> }
>
> - r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio);
> + r = kvm_gmem_make_private(kvm, slot, gfn, folio);
>
> folio_unlock(folio);
>
> --
> 2.55.0.141.g00534a21ce-goog
>