Re: [PATCH 14/21] KVM: Move x86's version of struct kvm_mmu_memory_cache to common code

[Ben Gardon]

On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> Move x86's 'struct kvm_mmu_memory_cache' to common code in anticipation
> of moving the entire x86 implementation code to common KVM and reusing
> it for arm64 and MIPS.  Add a new architecture specific asm/kvm_types.h
> to control the existence and parameters of the struct.  The new header
> is needed to avoid a chicken-and-egg problem with asm/kvm_host.h as all
> architectures define instances of the struct in their vCPU structs.
>
> Suggested-by: Christoffer Dall <christoffer.dall@xxxxxxx>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Reviewed-by: Ben Gardon <bgardon@xxxxxxxxxx>
> ---
>  arch/arm64/include/asm/kvm_types.h   |  6 ++++++
>  arch/mips/include/asm/kvm_types.h    |  5 +++++
>  arch/powerpc/include/asm/kvm_types.h |  5 +++++
>  arch/s390/include/asm/kvm_types.h    |  5 +++++
>  arch/x86/include/asm/kvm_host.h      | 13 -------------
>  arch/x86/include/asm/kvm_types.h     |  7 +++++++
>  include/linux/kvm_types.h            | 19 +++++++++++++++++++
>  7 files changed, 47 insertions(+), 13 deletions(-)
>  create mode 100644 arch/arm64/include/asm/kvm_types.h
>  create mode 100644 arch/mips/include/asm/kvm_types.h
>  create mode 100644 arch/powerpc/include/asm/kvm_types.h
>  create mode 100644 arch/s390/include/asm/kvm_types.h
>  create mode 100644 arch/x86/include/asm/kvm_types.h
>
> diff --git a/arch/arm64/include/asm/kvm_types.h b/arch/arm64/include/asm/kvm_types.h
> new file mode 100644
> index 000000000000..d0987007d581
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_types.h
> @@ -0,0 +1,6 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_ARM64_KVM_TYPES_H
> +#define _ASM_ARM64_KVM_TYPES_H
> +
> +#endif /* _ASM_ARM64_KVM_TYPES_H */
> +
> diff --git a/arch/mips/include/asm/kvm_types.h b/arch/mips/include/asm/kvm_types.h
> new file mode 100644
> index 000000000000..5efeb32a5926
> --- /dev/null
> +++ b/arch/mips/include/asm/kvm_types.h
> @@ -0,0 +1,5 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_MIPS_KVM_TYPES_H
> +#define _ASM_MIPS_KVM_TYPES_H
> +
> +#endif /* _ASM_MIPS_KVM_TYPES_H */
> diff --git a/arch/powerpc/include/asm/kvm_types.h b/arch/powerpc/include/asm/kvm_types.h
> new file mode 100644
> index 000000000000..f627eceaa314
> --- /dev/null
> +++ b/arch/powerpc/include/asm/kvm_types.h
> @@ -0,0 +1,5 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_POWERPC_KVM_TYPES_H
> +#define _ASM_POWERPC_KVM_TYPES_H
> +
> +#endif /* _ASM_POWERPC_KVM_TYPES_H */
> diff --git a/arch/s390/include/asm/kvm_types.h b/arch/s390/include/asm/kvm_types.h
> new file mode 100644
> index 000000000000..b66a81f8a354
> --- /dev/null
> +++ b/arch/s390/include/asm/kvm_types.h
> @@ -0,0 +1,5 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_S390_KVM_TYPES_H
> +#define _ASM_S390_KVM_TYPES_H
> +
> +#endif /* _ASM_S390_KVM_TYPES_H */
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index fb99e6776e27..8e8fea13b6c7 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -193,8 +193,6 @@ struct x86_exception;
>  enum x86_intercept;
>  enum x86_intercept_stage;
>
> -#define KVM_NR_MEM_OBJS 40
> -
>  #define KVM_NR_DB_REGS 4
>
>  #define DR6_BD         (1 << 13)
> @@ -245,17 +243,6 @@ enum x86_intercept_stage;
>
>  struct kvm_kernel_irq_routing_entry;
>
> -/*
> - * We don't want allocation failures within the mmu code, so we preallocate
> - * enough memory for a single page fault in a cache.
> - */
> -struct kvm_mmu_memory_cache {
> -       int nobjs;
> -       gfp_t gfp_zero;
> -       struct kmem_cache *kmem_cache;
> -       void *objects[KVM_NR_MEM_OBJS];
> -};
> -
>  /*
>   * the pages used as guest page table on soft mmu are tracked by
>   * kvm_memory_slot.arch.gfn_track which is 16 bits, so the role bits used
> diff --git a/arch/x86/include/asm/kvm_types.h b/arch/x86/include/asm/kvm_types.h
> new file mode 100644
> index 000000000000..08f1b57d3b62
> --- /dev/null
> +++ b/arch/x86/include/asm/kvm_types.h
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_X86_KVM_TYPES_H
> +#define _ASM_X86_KVM_TYPES_H
> +
> +#define KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE 40
> +
> +#endif /* _ASM_X86_KVM_TYPES_H */
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index 68e84cf42a3f..a7580f69dda0 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -20,6 +20,8 @@ enum kvm_mr_change;
>
>  #include <linux/types.h>
>
> +#include <asm/kvm_types.h>
> +
>  /*
>   * Address types:
>   *
> @@ -58,4 +60,21 @@ struct gfn_to_pfn_cache {
>         bool dirty;
>  };
>
> +#ifdef KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE
> +/*
> + * Memory caches are used to preallocate memory ahead of various MMU flows,
> + * e.g. page fault handlers.  Gracefully handling allocation failures deep in
> + * MMU flows is problematic, as is triggering reclaim, I/O, etc... while
> + * holding MMU locks.  Note, these caches act more like prefetch buffers than
> + * classical caches, i.e. objects are not returned to the cache on being freed.
> + */
> +struct kvm_mmu_memory_cache {
> +       int nobjs;
> +       gfp_t gfp_zero;
> +       struct kmem_cache *kmem_cache;
> +       void *objects[KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE];
> +};
> +#endif
> +
> +
>  #endif /* __KVM_TYPES_H__ */
> --
> 2.26.0
>