Re: [PATCH v3 1/3] x86/ioreq server(patch for 4.7): Rename p2m_mmio_write_dm to p2m_ioreq_server.

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

On 4/26/2016 1:01 AM, Paul Durrant wrote:
>> -----Original Message-----
>> From: George Dunlap [mailto:george.dunlap@citrix.com]
>> Sent: 25 April 2016 17:16
>> To: Yu, Zhang; Jan Beulich; Paul Durrant
>> Cc: Andrew Cooper; Wei Liu; Jun Nakajima; Kevin Tian; Zhiyuan Lv; xen-
>> devel@lists.xen.org; Keir (Xen.org); Tim (Xen.org)
>> Subject: Re: [Xen-devel] [PATCH v3 1/3] x86/ioreq server(patch for 4.7):
>> Rename p2m_mmio_write_dm to p2m_ioreq_server.
>>
>> On 25/04/16 16:53, Yu, Zhang wrote:
>>>
>>>
>>> On 4/25/2016 11:38 PM, Jan Beulich wrote:
>>>>>>> On 25.04.16 at 17:29, <Paul.Durrant@citrix.com> wrote:
>>>>>>  -----Original Message-----
>>>>>> From: Yu, Zhang [mailto:yu.c.zhang@linux.intel.com]
>>>>>> Sent: 25 April 2016 16:22
>>>>>> To: Paul Durrant; George Dunlap
>>>>>> Cc: xen-devel@lists.xen.org; Kevin Tian; Keir (Xen.org); Jun Nakajima;
>>>>>> Andrew Cooper; Tim (Xen.org); Lv, Zhiyuan; Jan Beulich; Wei Liu
>>>>>> Subject: Re: [Xen-devel] [PATCH v3 1/3] x86/ioreq server(patch for
>>>>>> 4.7):
>>>>>> Rename p2m_mmio_write_dm to p2m_ioreq_server.
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 4/25/2016 10:01 PM, Paul Durrant wrote:
>>>>>>>> -----Original Message-----
>>>>>>>> From: dunlapg@gmail.com [mailto:dunlapg@gmail.com] On Behalf
>> Of
>>>>>>>> George Dunlap
>>>>>>>> Sent: 25 April 2016 14:39
>>>>>>>> To: Yu Zhang
>>>>>>>> Cc: xen-devel@lists.xen.org; Kevin Tian; Keir (Xen.org); Jun
>>>>>>>> Nakajima;
>>>>>>>> Andrew Cooper; Tim (Xen.org); Paul Durrant; Lv, Zhiyuan; Jan
>>>>>>>> Beulich; Wei
>>>>>> Liu
>>>>>>>> Subject: Re: [Xen-devel] [PATCH v3 1/3] x86/ioreq server(patch for
>>>>>>>> 4.7):
>>>>>>>> Rename p2m_mmio_write_dm to p2m_ioreq_server.
>>>>>>>>
>>>>>>>> On Mon, Apr 25, 2016 at 11:35 AM, Yu Zhang
>>>>>> <yu.c.zhang@linux.intel.com>
>>>>>>>> wrote:
>>>>>>>>> Previously p2m type p2m_mmio_write_dm was introduced for
>> write-
>>>>>>>>> protected memory pages whose write operations are supposed to
>> be
>>>>>>>>> forwarded to and emulated by an ioreq server. Yet limitations of
>>>>>>>>> rangeset restrict the number of guest pages to be write-protected.
>>>>>>>>>
>>>>>>>>> This patch replaces the p2m type p2m_mmio_write_dm with a new
>>>>>> name:
>>>>>>>>> p2m_ioreq_server, which means this p2m type can be claimed by
>> one
>>>>>>>>> ioreq server, instead of being tracked inside the rangeset of ioreq
>>>>>>>>> server. Patches following up will add the related hvmop handling
>>>>>>>>> code which map/unmap type p2m_ioreq_server to/from an ioreq
>>>>>> server.
>>>>>>>>>
>>>>>>>>> changes in v3:
>>>>>>>>>   - According to Jan & George's comments, keep
>>>>>>>> HVMMEM_mmio_write_dm
>>>>>>>>>     for old xen interface versions, and replace it with
>>>>>>>>> HVMMEM_unused
>>>>>>>>>     for xen interfaces newer than 4.7.0; For p2m_ioreq_server, a
>> new
>>>>>>>>>     enum - HVMMEM_ioreq_server is introduced for the get/set
>> mem
>>>>>> type
>>>>>>>>>     interfaces;
>>>>>>>>>   - Add George's Reviewed-by and Acked-by from Tim & Andrew.
>>>>>>>>
>>>>>>>> Unfortunately these rather contradict each other -- I consider
>>>>>>>> Reviewed-by to only stick if the code I've specified hasn't changed
>>>>>>>> (or has only changed trivially).
>>>>>>>>
>>>>>>>> Also...
>>>>>>>>
>>>>>>>>>
>>>>>>>>> changes in v2:
>>>>>>>>>   - According to George Dunlap's comments, only rename the p2m
>> type,
>>>>>>>>>     with no behavior changes.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
>>>>>>>>> Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
>>>>>>>>> Acked-by: Tim Deegan <tim@xen.org>
>>>>>>>>> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>>>>>>>> Reviewed-by: George Dunlap <george.dunlap@citrix.com>
>>>>>>>>> Cc: Keir Fraser <keir@xen.org>
>>>>>>>>> Cc: Jan Beulich <jbeulich@suse.com>
>>>>>>>>> Cc: Andrew Cooper <andrew.cooper3@citrix.com>
>>>>>>>>> Cc: Jun Nakajima <jun.nakajima@intel.com>
>>>>>>>>> Cc: Kevin Tian <kevin.tian@intel.com>
>>>>>>>>> Cc: George Dunlap <george.dunlap@eu.citrix.com>
>>>>>>>>> Cc: Tim Deegan <tim@xen.org>
>>>>>>>>> ---
>>>>>>>>>  xen/arch/x86/hvm/hvm.c          | 14 ++++++++------
>>>>>>>>>  xen/arch/x86/mm/p2m-ept.c       |  2 +-
>>>>>>>>>  xen/arch/x86/mm/p2m-pt.c        |  2 +-
>>>>>>>>>  xen/arch/x86/mm/shadow/multi.c  |  2 +-
>>>>>>>>>  xen/include/asm-x86/p2m.h       |  4 ++--
>>>>>>>>>  xen/include/public/hvm/hvm_op.h |  8 +++++++-
>>>>>>>>>  6 files changed, 20 insertions(+), 12 deletions(-)
>>>>>>>>>
>>>>>>>>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
>>>>>>>>> index f24126d..874cb0f 100644
>>>>>>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>>>>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>>>>>>> @@ -1857,7 +1857,7 @@ int hvm_hap_nested_page_fault(paddr_t
>> gpa,
>>>>>>>> unsigned long gla,
>>>>>>>>>       */
>>>>>>>>>      if ( (p2mt == p2m_mmio_dm) ||
>>>>>>>>>           (npfec.write_access &&
>>>>>>>>> -          (p2m_is_discard_write(p2mt) || (p2mt ==
>>>>>> p2m_mmio_write_dm))) )
>>>>>>>>> +          (p2m_is_discard_write(p2mt) || (p2mt ==
>>>>>>>>> p2m_ioreq_server))) )
>>>>>>>>>      {
>>>>>>>>>          __put_gfn(p2m, gfn);
>>>>>>>>>          if ( ap2m_active )
>>>>>>>>> @@ -5499,8 +5499,8 @@ long do_hvm_op(unsigned long op,
>>>>>>>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>>>>>>>>              get_gfn_query_unlocked(d, a.pfn, &t);
>>>>>>>>>              if ( p2m_is_mmio(t) )
>>>>>>>>>                  a.mem_type =  HVMMEM_mmio_dm;
>>>>>>>>> -            else if ( t == p2m_mmio_write_dm )
>>>>>>>>> -                a.mem_type = HVMMEM_mmio_write_dm;
>>>>>>>>> +            else if ( t == p2m_ioreq_server )
>>>>>>>>> +                a.mem_type = HVMMEM_ioreq_server;
>>>>>>>>>              else if ( p2m_is_readonly(t) )
>>>>>>>>>                  a.mem_type =  HVMMEM_ram_ro;
>>>>>>>>>              else if ( p2m_is_ram(t) )
>>>>>>>>> @@ -5531,7 +5531,8 @@ long do_hvm_op(unsigned long op,
>>>>>>>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>>>>>>>>              [HVMMEM_ram_rw]  = p2m_ram_rw,
>>>>>>>>>              [HVMMEM_ram_ro]  = p2m_ram_ro,
>>>>>>>>>              [HVMMEM_mmio_dm] = p2m_mmio_dm,
>>>>>>>>> -            [HVMMEM_mmio_write_dm] = p2m_mmio_write_dm
>>>>>>>>> +            [HVMMEM_unused] = p2m_invalid,
>>>>>>>>> +            [HVMMEM_ioreq_server] = p2m_ioreq_server
>>>>>>>>>          };
>>>>>>>>>
>>>>>>>>>          if ( copy_from_guest(&a, arg, 1) )
>>>>>>>>> @@ -5555,7 +5556,8 @@ long do_hvm_op(unsigned long op,
>>>>>>>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>>>>>>>>               ((a.first_pfn + a.nr - 1) >
>>>>>>>>> domain_get_maximum_gpfn(d)) )
>>>>>>>>>              goto setmemtype_fail;
>>>>>>>>>
>>>>>>>>> -        if ( a.hvmmem_type >= ARRAY_SIZE(memtype) )
>>>>>>>>> +        if ( a.hvmmem_type >= ARRAY_SIZE(memtype) ||
>>>>>>>>> +             unlikely(a.hvmmem_type == HVMMEM_unused) )
>>>>>>>>>              goto setmemtype_fail;
>>>>>>>>>
>>>>>>>>>          while ( a.nr > start_iter )
>>>>>>>>> @@ -5579,7 +5581,7 @@ long do_hvm_op(unsigned long op,
>>>>>>>> XEN_GUEST_HANDLE_PARAM(void) arg)
>>>>>>>>>              }
>>>>>>>>>              if ( !p2m_is_ram(t) &&
>>>>>>>>>                   (!p2m_is_hole(t) || a.hvmmem_type !=
>>>>>>>>> HVMMEM_mmio_dm)
>>>>>>>> &&
>>>>>>>>> -                 (t != p2m_mmio_write_dm || a.hvmmem_type !=
>>>>>>>> HVMMEM_ram_rw) )
>>>>>>>>> +                 (t != p2m_ioreq_server || a.hvmmem_type !=
>>>>>>>> HVMMEM_ram_rw) )
>>>>>>>>>              {
>>>>>>>>>                  put_gfn(d, pfn);
>>>>>>>>>                  goto setmemtype_fail;
>>>>>>>>> diff --git a/xen/arch/x86/mm/p2m-ept.c
>> b/xen/arch/x86/mm/p2m-
>>>>>> ept.c
>>>>>>>>> index 3cb6868..380ec25 100644
>>>>>>>>> --- a/xen/arch/x86/mm/p2m-ept.c
>>>>>>>>> +++ b/xen/arch/x86/mm/p2m-ept.c
>>>>>>>>> @@ -171,7 +171,7 @@ static void ept_p2m_type_to_flags(struct
>>>>>>>> p2m_domain *p2m, ept_entry_t *entry,
>>>>>>>>>              entry->a = entry->d = !!cpu_has_vmx_ept_ad;
>>>>>>>>>              break;
>>>>>>>>>          case p2m_grant_map_ro:
>>>>>>>>> -        case p2m_mmio_write_dm:
>>>>>>>>> +        case p2m_ioreq_server:
>>>>>>>>>              entry->r = 1;
>>>>>>>>>              entry->w = entry->x = 0;
>>>>>>>>>              entry->a = !!cpu_has_vmx_ept_ad;
>>>>>>>>> diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-
>> pt.c
>>>>>>>>> index 3d80612..eabd2e3 100644
>>>>>>>>> --- a/xen/arch/x86/mm/p2m-pt.c
>>>>>>>>> +++ b/xen/arch/x86/mm/p2m-pt.c
>>>>>>>>> @@ -94,7 +94,7 @@ static unsigned long
>>>>>> p2m_type_to_flags(p2m_type_t
>>>>>>>> t, mfn_t mfn,
>>>>>>>>>      default:
>>>>>>>>>          return flags | _PAGE_NX_BIT;
>>>>>>>>>      case p2m_grant_map_ro:
>>>>>>>>> -    case p2m_mmio_write_dm:
>>>>>>>>> +    case p2m_ioreq_server:
>>>>>>>>>          return flags | P2M_BASE_FLAGS | _PAGE_NX_BIT;
>>>>>>>>>      case p2m_ram_ro:
>>>>>>>>>      case p2m_ram_logdirty:
>>>>>>>>> diff --git a/xen/arch/x86/mm/shadow/multi.c
>>>>>>>> b/xen/arch/x86/mm/shadow/multi.c
>>>>>>>>> index e5c8499..c81302a 100644
>>>>>>>>> --- a/xen/arch/x86/mm/shadow/multi.c
>>>>>>>>> +++ b/xen/arch/x86/mm/shadow/multi.c
>>>>>>>>> @@ -3225,7 +3225,7 @@ static int sh_page_fault(struct vcpu *v,
>>>>>>>>>
>>>>>>>>>      /* Need to hand off device-model MMIO to the device model */
>>>>>>>>>      if ( p2mt == p2m_mmio_dm
>>>>>>>>> -         || (p2mt == p2m_mmio_write_dm && ft ==
>> ft_demand_write) )
>>>>>>>>> +         || (p2mt == p2m_ioreq_server && ft == ft_demand_write) )
>>>>>>>>>      {
>>>>>>>>>          gpa = guest_walk_to_gpa(&gw);
>>>>>>>>>          goto mmio;
>>>>>>>>> diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-
>> x86/p2m.h
>>>>>>>>> index 5392eb0..ee2ea9c 100644
>>>>>>>>> --- a/xen/include/asm-x86/p2m.h
>>>>>>>>> +++ b/xen/include/asm-x86/p2m.h
>>>>>>>>> @@ -71,7 +71,7 @@ typedef enum {
>>>>>>>>>      p2m_ram_shared = 12,          /* Shared or sharable memory */
>>>>>>>>>      p2m_ram_broken = 13,          /* Broken page, access cause
>>>>>>>>> domain
>>>>>> crash
>>>>>>>> */
>>>>>>>>>      p2m_map_foreign  = 14,        /* ram pages from foreign
>>>>>>>>> domain */
>>>>>>>>> -    p2m_mmio_write_dm = 15,       /* Read-only; writes go to the
>>>>>>>>> device
>>>>>>>> model */
>>>>>>>>> +    p2m_ioreq_server = 15,
>>>>>>>>>  } p2m_type_t;
>>>>>>>>>
>>>>>>>>>  /* Modifiers to the query */
>>>>>>>>> @@ -112,7 +112,7 @@ typedef unsigned int p2m_query_t;
>>>>>>>>>                        | p2m_to_mask(p2m_ram_ro)         \
>>>>>>>>>                        | p2m_to_mask(p2m_grant_map_ro)   \
>>>>>>>>>                        | p2m_to_mask(p2m_ram_shared)     \
>>>>>>>>> -                      | p2m_to_mask(p2m_mmio_write_dm))
>>>>>>>>> +                      | p2m_to_mask(p2m_ioreq_server))
>>>>>>>>>
>>>>>>>>>  /* Write-discard types, which should discard the write
>>>>>>>>> operations */
>>>>>>>>>  #define P2M_DISCARD_WRITE_TYPES
>> (p2m_to_mask(p2m_ram_ro)     \
>>>>>>>>> diff --git a/xen/include/public/hvm/hvm_op.h
>>>>>>>> b/xen/include/public/hvm/hvm_op.h
>>>>>>>>> index 1606185..b3e45cf 100644
>>>>>>>>> --- a/xen/include/public/hvm/hvm_op.h
>>>>>>>>> +++ b/xen/include/public/hvm/hvm_op.h
>>>>>>>>> @@ -83,7 +83,13 @@ typedef enum {
>>>>>>>>>      HVMMEM_ram_rw,             /* Normal read/write guest RAM */
>>>>>>>>>      HVMMEM_ram_ro,             /* Read-only; writes are
>>>>>>>>> discarded */
>>>>>>>>>      HVMMEM_mmio_dm,            /* Reads and write go to the device
>>>>>> model
>>>>>>>> */
>>>>>>>>> -    HVMMEM_mmio_write_dm       /* Read-only; writes go to the
>>>>>>>>> device
>>>>>>>> model */
>>>>>>>>> +#if __XEN_INTERFACE_VERSION__ < 0x00040700
>>>>>>>>> +    HVMMEM_mmio_write_dm,      /* Read-only; writes go to the
>>>>>>>>> device
>>>>>>>> model */
>>>>>>>>> +#else
>>>>>>>>> +    HVMMEM_unused,             /* Placeholder; setting memory to
>>>>>>>>> this
>>>>>> type
>>>>>>>>> +                                  will fail for code after 4.7.0 */
>>>>>>>>> +#endif
>>>>>>>>> +    HVMMEM_ioreq_server
>>>>>>>>
>>>>>>>> Also, I don't think we've had a convincing argument for why this
>>>>>>>> patch
>>>>>>>> needs to be in 4.7.  The p2m name changes are internal only, and so
>>>>>>>> don't need to be made at all; and the old functionality will work as
>>>>>>>> well as it ever did.  Furthermore, the whole reason we're in this
>>>>>>>> situation is that we checked in a publicly-visible change to the
>>>>>>>> interface before it was properly ready; I think we should avoid
>>>>>>>> making
>>>>>>>> the same mistake this time.
>>>>>>>>
>>>>>>>> So personally I'd just leave this patch entirely for 4.8; but if Paul
>>>>>>>> and/or Jan have strong opinions, then I would say check in only a
>>>>>>>> patch to do the #if/#else/#endif, and leave both the p2m type
>> changes
>>>>>>>> and the new HVMMEM_ioreq_server enum for when the 4.8
>>>>>> development
>>>>>>>> window opens.
>>>>>>>>
>>>>>>>
>>>>>>> If the whole series is going in then I think this patch is ok. If
>>>>>>> this the
>>>>> only
>>>>>> patch that is going in for 4.7 then I thing we need the patch to
>>>>>> hvm_op.h to
>>>>>> deprecate the old type and that's it. We definitely should not
>>>>>> introduce an
>>>>>> implementation of the type HVMMEM_ioreq_server that has the same
>>>>>> hardcoded semantics as the old type and then change it.
>>>>>>> The p2m type changes are also wrong. That type needs to be left
>> alone,
>>>>>> presumably, so that anything using HVMMEM_mmio_write_dm and
>>>>>> compiled to the old interface version continues to function. I think
>>>>>> HVMMEM_ioreq_server needs to map to a new p2m type which
>> should be
>>>>>> introduced in patch #3.
>>>>>>>
>>>>>>
>>>>>> Sorry, I'm also confused now. :(
>>>>>>
>>>>>> Do we really want to introduce a new p2m type? Why?
>>>>>> My understanding of the previous agreement is that:
>>>>>> 1> We need the interface to work on old hypervisor for
>>>>>> HVMMEM_mmio_write_dm;
>>>>>> 2> We need the interface to return -EINVAL for new hypervisor
>>>>>> for HVMMEM_mmio_write_dm;
>>>>>> 3> We need the new type HVMMEM_ioreq_server to work on new
>>>>>> hypervisor;
>>>>>>
>>>>>> Did I miss something? Or I totally misunderstood?
>>>>>>
>>>>>
>>>>> I don't know. I'm confused too. What we definitely don't want to do
>>>>> is add a
>>>>> new HVMMEM type and have it map to the old behaviour, otherwise
>> we're no
>>>>> better off.
>>>>>
>>>>> The question I'm not clear on the answer to is what happens to old code:
>>>>>
>>>>> Should it continue to compile? If so, should it continue to run.
>>>>
>>>> We only need to be concerned about the "get type" functionality,
>>>> as that's the only thing an arbitrary guest can use. If the
>>>> hypercall simply never returns the old type, then old code will
>>>> still work (it'll just have some dead code on new Xen), and hence
>>>> it compiling against the older interface is fine (and, from general
>>>> considerations, a requirement).
>>>>
>>>
>>> Thanks Jan. And I think the answer is yes. The new hypervisor will
>>> only return HVMMEM_ioreq_server, which is a different value now.
>>
>> Right -- but we can't check in this entire series for 4.7; however, Paul
>> would like to make it clear that HVMMEM_mmio_write_dm is deprecated;
>> so
>> we need a patch which does the #ifdef/#else/#endif clause, and then
>> everything else necessary to make sure that things compile properly
>> either way, but no p2m changes or additional functionality.
>>
>
> For clarity, do you expect any existing use of HVMMEM_mmio_write_dm to continue to *function*? I agree that things should continue to build, but if they don't need to function then the now redundant p2m type should be removed IMO and any attempt to set a page to HVMMEM_mmio_write_dm (or the new HVMMEM_unused) name should result in -EINVAL. What is your position on this?
>

Thanks, Paul.
My expectation is that HVMMEM_mmio_write_dm shall fail in new xen
version, but I do not think we need to remove the p2m type, just
rename it could be OK.

>   Paul
>
>>  -George

Yu

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