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

["Yu, Zhang" <yu.c.zhang@linux.intel.com>]

On 4/8/2016 9:33 PM, Andrew Cooper wrote:
> 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?
>

The 'size' is set in hvmemul_linear_mmio_access(), to insure offset + 
size will not cross 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.
>
Oh, guess I should use uint16_t hvmmem_type(any maybe some pad if
necessary).
Thanks for pointing this out, Andrew. :)

> ~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__ */
>>
>>   /*
>
>

B.R.
Yu

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