Re: [RFC PATCH v2 02/21] RAMBlock: Add support of KVM private gmem

[Daniel P . Berrangé]

On Wed, Sep 13, 2023 at 11:50:58PM -0400, Xiaoyao Li wrote:
> From: Chao Peng <chao.p.peng@linux.intel.com>
> 
> Add KVM gmem support to RAMBlock so both normal hva based memory
> and kvm gmem fd based private memory can be associated in one RAMBlock.
> 
> Introduce new flag RAM_KVM_GMEM. It calls KVM ioctl to create private
> gmem for the RAMBlock when it's set.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>  accel/kvm/kvm-all.c     | 17 +++++++++++++++++
>  include/exec/memory.h   |  3 +++
>  include/exec/ramblock.h |  1 +
>  include/sysemu/kvm.h    |  2 ++
>  softmmu/physmem.c       | 18 +++++++++++++++---
>  5 files changed, 38 insertions(+), 3 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 60aacd925393..185ae16d9620 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -4225,3 +4225,20 @@ void query_stats_schemas_cb(StatsSchemaList **result, 
> Error **errp)
>          query_stats_schema_vcpu(first_cpu, &stats_args);
>      }
>  }
> +
> +int kvm_create_guest_memfd(uint64_t size, uint64_t flags, Error **errp)
> +{
> +    int fd;
> +    struct kvm_create_guest_memfd gmem = {
> +        .size = size,
> +        /* TODO: to decide whether KVM_GUEST_MEMFD_ALLOW_HUGEPAGE is 
> supported */
> +        .flags = flags,
> +    };
> +
> +    fd = kvm_vm_ioctl(kvm_state, KVM_CREATE_GUEST_MEMFD, &gmem);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "%s: error creating kvm gmem\n", 
> __func__);
> +    }
> +
> +    return fd;
> +}
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 68284428f87c..227cb2578e95 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -235,6 +235,9 @@ typedef struct IOMMUTLBEvent {
>  /* RAM is an mmap-ed named file */
>  #define RAM_NAMED_FILE (1 << 9)
>  
> +/* RAM can be private that has kvm gmem backend */
> +#define RAM_KVM_GMEM    (1 << 10)
> +
>  static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
>                                         IOMMUNotifierFlag flags,
>                                         hwaddr start, hwaddr end,
> diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
> index 69c6a5390293..0d158b3909c9 100644
> --- a/include/exec/ramblock.h
> +++ b/include/exec/ramblock.h
> @@ -41,6 +41,7 @@ struct RAMBlock {
>      QLIST_HEAD(, RAMBlockNotifier) ramblock_notifiers;
>      int fd;
>      uint64_t fd_offset;
> +    int gmem_fd;
>      size_t page_size;
>      /* dirty bitmap used during migration */
>      unsigned long *bmap;

You're adding a file descriptor to RAMBlock, but I don't see
anything in this patch that ever calls close(gmem_fd) when the
RAMBlock is released. Presuambly reclaim_ramblock() needs to
deal with this ?


With regards,
Daniel
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