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

Ben Gardon
2020-06-10T21:58:38Z

On Wed, Jun 10, 2020 at 12:01 PM Ben Gardon <bgardon@google.com> wrote:
>
> On Fri, Jun 5, 2020 at 2:39 PM Sean Christopherson
> <sean.j.christopherson@intel.com> 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@arm.com>
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Reviewed-by: Ben Gardon <bgardon@google.com>
> > ---
> > 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
> > -
Oops I didn't catch this on my first read through, but in patch 16 in
this series I see some references to KVM_NR_MEM_OBJS being removed. As
a result I would not expect this patch to build. Other references to
this value should probably replaced with
KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE as well.
> > #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
> >