Re: [PATCH v2 3/3] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 31/03/16 11:53, Yu Zhang wrote:
> A new HVMOP - HVMOP_map_mem_type_to_ioreq_server, is added to
> let one ioreq server claim/disclaim its responsibility for the
> handling of guest pages with p2m type p2m_ioreq_server. Users
> of this HVMOP can specify whether the p2m_ioreq_server is supposed
> to handle write accesses or read ones or both in a parameter named
> flags. For now, we only support one ioreq server for this p2m type,
> so once an ioreq server has claimed its ownership, subsequent calls
> of the HVMOP_map_mem_type_to_ioreq_server will fail. Users can also
> disclaim the ownership of guest ram pages with this p2m type, by
> triggering this new HVMOP, with ioreq server id set to the current
> owner's and flags parameter set to 0.
>
> For now, both HVMOP_map_mem_type_to_ioreq_server and p2m_ioreq_server
> are only supported for HVMs with HAP enabled.
>
> Note that flags parameter(if not 0) of this HVMOP only indicates
> which kind of memory accesses are to be forwarded to an ioreq server,
> it has impact on the access rights of guest ram pages, but are not
> the same. Due to hardware limitations, if only write operations are
> to be forwarded, read ones will be performed at full speed, with
> no hypervisor intervention. But if read ones are to be forwarded to
> an ioreq server, writes will inevitably be trapped into hypervisor,
> which means significant performance impact.
>
> Also note that this HVMOP_map_mem_type_to_ioreq_server will not
> change the p2m type of any guest ram page, until HVMOP_set_mem_type
> is triggered. So normally the steps should be the backend driver
> first claims its ownership of guest ram pages with p2m_ioreq_server
> type, and then sets the memory type to p2m_ioreq_server for specified
> guest ram pages.
>
> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> Cc: Keir Fraser <keir@xen.org>
> Cc: Jan Beulich <jbeulich@suse.com>
> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
> Cc: George Dunlap <george.dunlap@eu.citrix.com>
> Cc: Jun Nakajima <jun.nakajima@intel.com>
> Cc: Kevin Tian <kevin.tian@intel.com>
> Cc: Tim Deegan <tim@xen.org>
> ---
>  xen/arch/x86/hvm/emulate.c       | 125 +++++++++++++++++++++++++++++++++++++--
>  xen/arch/x86/hvm/hvm.c           |  95 +++++++++++++++++++++++++++--
>  xen/arch/x86/mm/hap/nested_hap.c |   2 +-
>  xen/arch/x86/mm/p2m-ept.c        |  14 ++++-
>  xen/arch/x86/mm/p2m-pt.c         |  25 +++++---
>  xen/arch/x86/mm/p2m.c            |  82 +++++++++++++++++++++++++
>  xen/arch/x86/mm/shadow/multi.c   |   3 +-
>  xen/include/asm-x86/p2m.h        |  36 +++++++++--
>  xen/include/public/hvm/hvm_op.h  |  37 ++++++++++++
>  9 files changed, 395 insertions(+), 24 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
> index ddc8007..77a4793 100644
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -94,11 +94,69 @@ static const struct hvm_io_handler null_handler = {
>      .ops = &null_ops
>  };
>  
> +static int mem_read(const struct hvm_io_handler *io_handler,
> +                    uint64_t addr,
> +                    uint32_t size,
> +                    uint64_t *data)
> +{
> +    struct domain *currd = current->domain;
> +    unsigned long gmfn = paddr_to_pfn(addr);
> +    unsigned long offset = addr & ~PAGE_MASK;
> +    struct page_info *page = get_page_from_gfn(currd, gmfn, NULL, P2M_UNSHARE);
> +    uint8_t *p;
> +
> +    if ( !page )
> +        return X86EMUL_UNHANDLEABLE;
> +
> +    p = __map_domain_page(page);
> +    p += offset;
> +    memcpy(data, p, size);

What happens when offset + size crosses the page boundary?


> diff --git a/xen/include/public/hvm/hvm_op.h b/xen/include/public/hvm/hvm_op.h
> index a1eae52..d46f186 100644
> --- a/xen/include/public/hvm/hvm_op.h
> +++ b/xen/include/public/hvm/hvm_op.h
> @@ -489,6 +489,43 @@ struct xen_hvm_altp2m_op {
>  typedef struct xen_hvm_altp2m_op xen_hvm_altp2m_op_t;
>  DEFINE_XEN_GUEST_HANDLE(xen_hvm_altp2m_op_t);
>  
> +#if defined(__XEN__) || defined(__XEN_TOOLS__)
> +
> +/*
> + * HVMOP_map_mem_type_to_ioreq_server : map or unmap the IOREQ Server <id>
> + *                                      to specific memroy type <type>
> + *                                      for specific accesses <flags>
> + *
> + * Note that if only write operations are to be forwarded to an ioreq server,
> + * read operations will be performed with no hypervisor intervention. But if
> + * flags indicates that read operations are to be forwarded to an ioreq server,
> + * write operations will inevitably be trapped into hypervisor, whether they
> + * are emulated by hypervisor or forwarded to ioreq server depends on the flags
> + * setting. This situation means significant performance impact.
> + */
> +#define HVMOP_map_mem_type_to_ioreq_server 26
> +struct xen_hvm_map_mem_type_to_ioreq_server {
> +    domid_t domid;      /* IN - domain to be serviced */
> +    ioservid_t id;      /* IN - ioreq server id */
> +    hvmmem_type_t type; /* IN - memory type */

hvmmem_type_t is an enum and doesn't have a fixed width.  It can't be
used in the public API.

You also have some implicit padding holes as a result of the layout.

~Andrew

> +    uint32_t flags;     /* IN - types of accesses to be forwarded to the
> +                           ioreq server. flags with 0 means to unmap the
> +                           ioreq server */
> +#define _HVMOP_IOREQ_MEM_ACCESS_READ 0
> +#define HVMOP_IOREQ_MEM_ACCESS_READ \
> +    (1u << _HVMOP_IOREQ_MEM_ACCESS_READ)
> +
> +#define _HVMOP_IOREQ_MEM_ACCESS_WRITE 1
> +#define HVMOP_IOREQ_MEM_ACCESS_WRITE \
> +    (1u << _HVMOP_IOREQ_MEM_ACCESS_WRITE)
> +};
> +typedef struct xen_hvm_map_mem_type_to_ioreq_server
> +    xen_hvm_map_mem_type_to_ioreq_server_t;
> +DEFINE_XEN_GUEST_HANDLE(xen_hvm_map_mem_type_to_ioreq_server_t);
> +
> +#endif /* defined(__XEN__) || defined(__XEN_TOOLS__) */
> +
> +
>  #endif /* __XEN_PUBLIC_HVM_HVM_OP_H__ */
>  
>  /*


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