Re: [Xen-devel] [PATCH v2 02/11] acpi: Define ACPI IO registers for PVH guests

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 11/09/2016 04:01 PM, Boris Ostrovsky wrote:
> On 11/09/2016 02:58 PM, Andrew Cooper wrote:
>> On 09/11/16 15:14, Boris Ostrovsky wrote:
>>> On 11/09/2016 09:59 AM, Andrew Cooper wrote:
>>>>> diff --git a/xen/include/public/hvm/ioreq.h 
>>>>> b/xen/include/public/hvm/ioreq.h
>>>>> index 2e5809b..e3fa704 100644
>>>>> --- a/xen/include/public/hvm/ioreq.h
>>>>> +++ b/xen/include/public/hvm/ioreq.h
>>>>> @@ -24,6 +24,8 @@
>>>>>  #ifndef _IOREQ_H_
>>>>>  #define _IOREQ_H_
>>>>>  
>>>>> +#include "hvm_info_table.h" /* HVM_MAX_VCPUS */
>>>>> +
>>>>>  #define IOREQ_READ      1
>>>>>  #define IOREQ_WRITE     0
>>>>>  
>>>>> @@ -124,6 +126,17 @@ typedef struct buffered_iopage buffered_iopage_t;
>>>>>  #define ACPI_GPE0_BLK_ADDRESS        ACPI_GPE0_BLK_ADDRESS_V0
>>>>>  #define ACPI_GPE0_BLK_LEN            ACPI_GPE0_BLK_LEN_V0
>>>>>  
>>>>> +#define ACPI_PM1A_EVT_BLK_LEN        0x04
>>>>> +#define ACPI_PM1A_CNT_BLK_LEN        0x02
>>>>> +#define ACPI_PM_TMR_BLK_LEN          0x04
>>>>> +
>>>>> +/* Location of online VCPU bitmap. */
>>>>> +#define ACPI_CPU_MAP                 0xaf00
>>>>> +#define ACPI_CPU_MAP_LEN             ((HVM_MAX_VCPUS / 8) + \
>>>>> +                                      ((HVM_MAX_VCPUS & 7) ? 1 : 0))
>>>>> +#if ACPI_CPU_MAP + ACPI_CPU_MAP_LEN >= ACPI_GPE0_BLK_ADDRESS_V1
>>>>> +#error "ACPI_CPU_MAP is too big"
>>>>> +#endif
>>>> Why is this in ioreq.h?  It has nothing to do with ioreq's.
>>>>
>>>> The current ACPI bits in here are to do with the qemu ACPI interface,
>>>> not the Xen ACPI interface.
>>>>
>>>> Also, please can we avoid hard-coding the location of the map in the
>>>> hypervisor ABI.  These constants make it impossible to ever extend the
>>>> number of HVM vcpus at a future date.
>>> The first three logically belong here because corresponding blocks'
>>> addresses are defined right above.
>> They have no relationship to the ones above, other than their name.
> They describe the same object --- for example
> ACPI_PM1A_CNT_BLK_ADDRESS_V1 and (new) ACPI_PM1A_CNT_BLK_LEN describe
> pm1a control.
>
> As far as definitions being there for qemu interface only ---
> ACPI_PM1A_CNT_BLK_ADDRESS_V1, for example, is used only by hvmloader and
> libacpi.
>
>
>>> ACPI_CPU_MAP has to be seen by both the toolstack (libacpi) and the
>>> hypervisor (and qemu as well, although it is defined as
>>> PIIX4_CPU_HOTPLUG_IO_BASE).
>>>
>>> Where do you think it should go then?
>> This highlights a reoccurring problem in Xen which desperately needs
>> fixing, but still isn't high enough on my TODO list to tackle yet.
>>
>> There is no central registration of claims on domain resources.  This is
>> the root cause of memory accounting problems for HVM guests.
>>
>>
>> The way I planned to fix this was to have Xen maintain a registry of
>> domains physical resources which ends up looking very much like
>> /proc/io{mem,ports}.  There will be a hypercall interface for querying
>> this information, and for a toolstack and device model to modify it.
>>
>> The key point is that Xen needs to be authoritative source of
>> information pertaining to layout, rather than the current fiasco we have
>> of the toolstack, qemu and hvmloader all thinking they know and control
>> what's going on.  This fixes several current unknowns which have caused
>> real problems, such as whether a domain was told about certain RMRRs
>> when it booted, or how many PXEROMs qemu tried to fit into the physmap.
>>
>> This information (eventually, when I get Xen-level migration v2 sorted)
>> needs to move at the head of the migration stream.
>>
>> The way I would envisage this working is that on domain create, Xen
>> makes a blank map indicating that all space is free.  By selecting
>> X86_EMUL_APCI_*, Xen takes out an allocation when it wires up the ioport
>> handler.
>>
>> Later, when constructing the ACPI tables, the toolstack reads the
>> current ioport allocations and can see exactly which ports are reserved
>> for what.
>>
>>
>> Now, I understand that lumbering you with this work as a prerequisite
>> would be unfair.
>>
>> Therefore, I will accept an alternative of hiding all these definitions
>> behind __XEN_TOOLS__ so the longterm fix can be introduced in a
>> compatible manner in the future.
>
> __XEN_TOOLS__ or (__XEN__ || __XEN_TOOLS__) ? Because both the toolstack
> and the hypervisor want to see them.
>
>
>> That said, I am still certain that they shouldn't live in ioreq.h, as
>> they have nothing to do with Qemu.
> None of the existing files looks (to me) much better in terms of being
> more appropriate. include/public/arch-x86/xen.h?

Andrew, ping on these two questions.

-boris

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