Re: [PATCH 04/11] KVM: page track: add the framework of guest page tracking

[Kai Huang <kai.huang@linux.intel.com>]

Hi Guangrong,

I am starting to review this series, and should have some comments or 
questions, you can determine whether they are valuable :)

See  below.

On 12/01/2015 02:26 AM, Xiao Guangrong wrote:
> The array, gfn_track[mode][gfn], is introduced in memory slot for every
> guest page, this is the tracking count for the gust page on different
> modes. If the page is tracked then the count is increased, the page is
> not tracked after the count reaches zero
>
> Two callbacks, kvm_page_track_create_memslot() and
> kvm_page_track_free_memslot() are implemented in this patch, they are
> internally used to initialize and reclaim the memory of the array
>
> Currently, only write track mode is supported
>
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
>   arch/x86/include/asm/kvm_host.h       |  2 ++
>   arch/x86/include/asm/kvm_page_track.h | 13 ++++++++
>   arch/x86/kvm/Makefile                 |  3 +-
>   arch/x86/kvm/page_track.c             | 58 +++++++++++++++++++++++++++++++++++
>   arch/x86/kvm/x86.c                    |  5 +++
>   5 files changed, 80 insertions(+), 1 deletion(-)
>   create mode 100644 arch/x86/include/asm/kvm_page_track.h
>   create mode 100644 arch/x86/kvm/page_track.c
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 5aa2dcc..afff1f1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -32,6 +32,7 @@
>   #include <asm/mtrr.h>
>   #include <asm/msr-index.h>
>   #include <asm/asm.h>
> +#include <asm/kvm_page_track.h>
>   
>   #define KVM_MAX_VCPUS 255
>   #define KVM_SOFT_MAX_VCPUS 160
> @@ -612,6 +613,7 @@ struct kvm_lpage_info {
>   struct kvm_arch_memory_slot {
>   	struct kvm_rmap_head *rmap[KVM_NR_PAGE_SIZES];
>   	struct kvm_lpage_info *lpage_info[KVM_NR_PAGE_SIZES - 1];
> +	int *gfn_track[KVM_PAGE_TRACK_MAX];
>   };
>   
>   /*
> diff --git a/arch/x86/include/asm/kvm_page_track.h b/arch/x86/include/asm/kvm_page_track.h
> new file mode 100644
> index 0000000..347d5c9
> --- /dev/null
> +++ b/arch/x86/include/asm/kvm_page_track.h
> @@ -0,0 +1,13 @@
> +#ifndef _ASM_X86_KVM_PAGE_TRACK_H
> +#define _ASM_X86_KVM_PAGE_TRACK_H
> +
> +enum kvm_page_track_mode {
> +	KVM_PAGE_TRACK_WRITE,
> +	KVM_PAGE_TRACK_MAX,
> +};
> +
> +int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
> +				  unsigned long npages);
> +void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
> +				 struct kvm_memory_slot *dont);
> +#endif
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index a1ff508..464fa47 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -13,9 +13,10 @@ kvm-$(CONFIG_KVM_ASYNC_PF)	+= $(KVM)/async_pf.o
>   
>   kvm-y			+= x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
>   			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
> -			   hyperv.o
> +			   hyperv.o page_track.o
>   
>   kvm-$(CONFIG_KVM_DEVICE_ASSIGNMENT)	+= assigned-dev.o iommu.o
> +
>   kvm-intel-y		+= vmx.o pmu_intel.o
>   kvm-amd-y		+= svm.o pmu_amd.o
>   
> diff --git a/arch/x86/kvm/page_track.c b/arch/x86/kvm/page_track.c
> new file mode 100644
> index 0000000..0338d36
> --- /dev/null
> +++ b/arch/x86/kvm/page_track.c
> @@ -0,0 +1,58 @@
> +/*
> + * Support KVM gust page tracking
> + *
> + * This feature allows us to track page access in guest. Currently, only
> + * write access is tracked.
> + *
> + * Copyright(C) 2015 Intel Corporation.
> + *
> + * Author:
> + *   Xiao Guangrong <guangrong.xiao@linux.intel.com>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + */
> +
> +#include <linux/kvm_host.h>
> +#include <asm/kvm_host.h>
> +#include <asm/kvm_page_track.h>
> +
> +#include "mmu.h"
> +
> +static void page_track_slot_free(struct kvm_memory_slot *slot)
> +{
> +	int i;
> +
> +	for (i = 0; i < KVM_PAGE_TRACK_MAX; i++)
> +		if (slot->arch.gfn_track[i]) {
> +			kvfree(slot->arch.gfn_track[i]);
> +			slot->arch.gfn_track[i] = NULL;
> +		}
> +}
> +
> +int kvm_page_track_create_memslot(struct kvm_memory_slot *slot,
> +				  unsigned long npages)
> +{
> +	int  i, pages = gfn_to_index(slot->base_gfn + npages - 1,
> +				  slot->base_gfn, PT_PAGE_TABLE_LEVEL) + 1;
> +
> +	for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
> +		slot->arch.gfn_track[i] = kvm_kvzalloc(pages *
> +					    sizeof(*slot->arch.gfn_track[i]));
> +		if (!slot->arch.gfn_track[i])
> +			goto track_free;
> +	}
> +
> +	return 0;
> +
> +track_free:
> +	page_track_slot_free(slot);
> +	return -ENOMEM;
> +}
Is it necessary to use the 'unsigned long npages' pareameter? In my 
understanding you are going to track all GFNs in the memory slot anyway, 
right? If you want to keep npages, I think it's better to add a base_gfn 
as well otherwise you are assuming you are going to track the npages GFN 
starting from slot->base_gfn.

> +
> +void kvm_page_track_free_memslot(struct kvm_memory_slot *free,
> +				 struct kvm_memory_slot *dont)
> +{
> +	if (!dont || free->arch.gfn_track != dont->arch.gfn_track)
> +		page_track_slot_free(free);
> +}
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c04987e..ad4888a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -7838,6 +7838,8 @@ void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *free,
>   			free->arch.lpage_info[i - 1] = NULL;
>   		}
>   	}
> +
> +	kvm_page_track_free_memslot(free, dont);
>   }
>   
>   int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
> @@ -7886,6 +7888,9 @@ int kvm_arch_create_memslot(struct kvm *kvm, struct kvm_memory_slot *slot,
>   		}
>   	}
>   
> +	if (kvm_page_track_create_memslot(slot, npages))
> +		goto out_free;
> +
Looks essentially you are allocating one int for all GFNs of the slot 
unconditionally. In my understanding for most of memory slots, we are 
not going to track them, so isn't it going to be wasteful of memory?

Thanks,
-Kai
>   	return 0;
>   
>   out_free: