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 4/25/2016 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?

B.R.
Yu

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