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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.04.16 at 14:20, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 11/04/16 12:14, Yu, Zhang wrote:
>>
>>
>> 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@xxxxxxxxxx>
>>>> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
>>>> Cc: Keir Fraser <keir@xxxxxxx>
>>>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>>>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>>>> Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
>>>> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
>>>> Cc: Tim Deegan <tim@xxxxxxx>
>>>> ---
>>>>   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.
> 
> Ok, in which case please
> 
> ASSERT(offset + size < PAGE_SIZE)

<=

Jan

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