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From: Oleksandr <olekstysh@gmail.com>
To: Julien Grall <julien@xen.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	George Dunlap <george.dunlap@citrix.com>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
	Julien Grall <julien.grall@arm.com>,
	Jan Beulich <jbeulich@suse.com>,
	xen-devel@lists.xenproject.org,
	Daniel De Graaf <dgdegra@tycho.nsa.gov>,
	Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features
Date: Wed, 5 Aug 2020 18:41:06 +0300	[thread overview]
Message-ID: <ba4069dd-cc87-921b-6b52-dc51ff7bb13d@gmail.com> (raw)
In-Reply-To: <8e8a394c-bd2a-4444-9f4b-e022c59e0f81@xen.org>


On 05.08.20 12:32, Julien Grall wrote:

Hi Julien.

> Hi Stefano,
>
> On 05/08/2020 00:22, Stefano Stabellini wrote:
>> On Mon, 3 Aug 2020, Oleksandr Tyshchenko wrote:
>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>>>
>>> This patch makes possible to forward Guest MMIO accesses
>>> to a device emulator on Arm and enables that support for
>>> Arm64.
>>>
>>> Also update XSM code a bit to let DM op be used on Arm.
>>> New arch DM op will be introduced in the follow-up patch.
>>>
>>> Please note, at the moment build on Arm32 is broken
>>> (see cmpxchg usage in hvm_send_buffered_ioreq()) if someone
>>
>> Speaking of buffered_ioreq, if I recall correctly, they were only used
>> for VGA-related things on x86. It looks like it is still true.
>>
>> If so, do we need it on ARM? Note that I don't think we can get rid of
>> it from the interface as it is baked into ioreq, but it might be
>> possible to have a dummy implementation on ARM. Or maybe not: looking at
>> xen/common/hvm/ioreq.c it looks like it would be difficult to
>> disentangle bufioreq stuff from the rest of the code.
>
> We possibly don't need it right now. However, this could possibly be 
> used in the future (e.g. virtio notification doorbell).
>
>>> @@ -2275,6 +2282,16 @@ static void check_for_vcpu_work(void)
>>>    */
>>>   void leave_hypervisor_to_guest(void)
>>>   {
>>> +#ifdef CONFIG_IOREQ_SERVER
>>> +    /*
>>> +     * XXX: Check the return. Shall we call that in
>>> +     * continue_running and context_switch instead?
>>> +     * The benefits would be to avoid calling
>>> +     * handle_hvm_io_completion on every return.
>>> +     */
>>
>> Yeah, that could be a simple and good optimization
>
> Well, it is not simple as it is sounds :). handle_hvm_io_completion() 
> is the function in charge to mark the vCPU as waiting for I/O. So we 
> would at least need to split the function.
>
> I wrote this TODO because I wasn't sure about the complexity of 
> handle_hvm_io_completion(current). Looking at it again, the main 
> complexity is the looping over the IOREQ servers.
>
> I think it would be better to optimize handle_hvm_io_completion() 
> rather than trying to hack the context_switch() or continue_running().
>
> [...]
>
>>> diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
>>> index 5fdb6e8..5823f11 100644
>>> --- a/xen/include/asm-arm/p2m.h
>>> +++ b/xen/include/asm-arm/p2m.h
>>> @@ -385,10 +385,11 @@ static inline int set_foreign_p2m_entry(struct 
>>> domain *d, unsigned long gfn,
>>>                                           mfn_t mfn)
>>>   {
>>>       /*
>>> -     * NOTE: If this is implemented then proper reference counting of
>>> -     *       foreign entries will need to be implemented.
>>> +     * XXX: handle properly reference. It looks like the page may 
>>> not always
>>> +     * belong to d.
>>
>> Just as a reference, and without taking away anything from the comment,
>> I think that QEMU is doing its own internal reference counting for these
>> mappings.
>
> I am not sure how this matters here? We can't really trust the DM to 
> do the right thing if it is not running in dom0.
>
> But, IIRC, the problem is some of the pages doesn't belong to do a 
> domain, so it is not possible to treat them as foreign mapping (e.g. 
> you wouldn't be able to grab a reference). This investigation was done 
> a couple of years ago, so this may have changed in recent Xen.
>
> As a side note, I am a bit surprised to see most of my original TODOs 
> present in the code. What is the plan to solve them?
The plan is to solve most critical TODOs in current series, and rest in 
follow-up series if no objections of course. Any pointers how to solve 
them properly would be much appreciated. Unfortunately, now I have a 
weak understanding how they should be fixed. I see at least 3 major TODO 
here:

1. handle properly reference in set_foreign_p2m_entry()
2. optimize handle_hvm_io_completion()
3. hande properly IO_RETRY in try_fwd_ioserv()


-- 
Regards,

Oleksandr Tyshchenko



  reply	other threads:[~2020-08-05 15:41 UTC|newest]

Thread overview: 140+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-03 18:21 [RFC PATCH V1 00/12] IOREQ feature (+ virtio-mmio) on Arm Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 01/12] hvm/ioreq: Make x86's IOREQ feature common Oleksandr Tyshchenko
2020-08-04  7:45   ` Paul Durrant
2020-08-04 11:10     ` Oleksandr
2020-08-04 11:23       ` Paul Durrant
2020-08-04 11:51         ` Oleksandr
2020-08-04 13:18           ` Paul Durrant
2020-08-04 13:52       ` Julien Grall
2020-08-04 15:41         ` Jan Beulich
2020-08-04 19:11         ` Stefano Stabellini
2020-08-05  7:01           ` Jan Beulich
2020-08-06  0:37             ` Stefano Stabellini
2020-08-06  6:59               ` Jan Beulich
2020-08-06 20:32                 ` Stefano Stabellini
2020-08-07 13:19                   ` Oleksandr
2020-08-07 16:45               ` Oleksandr
2020-08-07 21:50                 ` Stefano Stabellini
2020-08-07 22:19                   ` Oleksandr
2020-08-10 13:41                     ` Oleksandr
2020-08-10 23:34                       ` Stefano Stabellini
2020-08-11  9:19                         ` Julien Grall
2020-08-11 10:10                           ` Oleksandr
2020-08-11 22:47                             ` Stefano Stabellini
2020-08-12 14:35                               ` Oleksandr
2020-08-12 23:08                                 ` Stefano Stabellini
2020-08-13 20:16                                   ` Julien Grall
2020-08-07 23:45                   ` Oleksandr
2020-08-10 23:34                     ` Stefano Stabellini
2020-08-05  8:33           ` Julien Grall
2020-08-06  0:37             ` Stefano Stabellini
2020-08-06  9:45               ` Julien Grall
2020-08-06 23:48                 ` Stefano Stabellini
2020-08-10 19:20                   ` Julien Grall
2020-08-10 23:34                     ` Stefano Stabellini
2020-08-11 11:28                       ` Julien Grall
2020-08-11 22:48                         ` Stefano Stabellini
2020-08-12  8:19                           ` Julien Grall
2020-08-20 19:14                             ` Oleksandr
2020-08-21  0:53                               ` Stefano Stabellini
2020-08-21 18:54                                 ` Julien Grall
2020-08-05 13:30   ` Julien Grall
2020-08-06 11:37     ` Oleksandr
2020-08-10 16:29       ` Julien Grall
2020-08-10 17:28         ` Oleksandr
2020-08-05 16:15   ` Andrew Cooper
2020-08-06  8:20     ` Oleksandr
2020-08-15 17:30   ` Julien Grall
2020-08-16 19:37     ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 02/12] hvm/dm: Make x86's DM " Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 03/12] xen/mm: Make x86's XENMEM_resource_ioreq_server handling common Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features Oleksandr Tyshchenko
2020-08-04  7:49   ` Paul Durrant
2020-08-04 14:01     ` Julien Grall
2020-08-04 23:22       ` Stefano Stabellini
2020-08-15 17:56       ` Julien Grall
2020-08-17 14:36         ` Oleksandr
2020-08-04 23:22   ` Stefano Stabellini
2020-08-05  7:05     ` Jan Beulich
2020-08-05 16:41       ` Stefano Stabellini
2020-08-05 19:45         ` Oleksandr
2020-08-05  9:32     ` Julien Grall
2020-08-05 15:41       ` Oleksandr [this message]
2020-08-06 10:19         ` Julien Grall
2020-08-10 18:09       ` Oleksandr
2020-08-10 18:21         ` Oleksandr
2020-08-10 19:00         ` Julien Grall
2020-08-10 20:29           ` Oleksandr
2020-08-10 22:37             ` Julien Grall
2020-08-11  6:13               ` Oleksandr
2020-08-12 15:08                 ` Oleksandr
2020-08-11 17:09       ` Oleksandr
2020-08-11 17:50         ` Julien Grall
2020-08-13 18:41           ` Oleksandr
2020-08-13 20:36             ` Julien Grall
2020-08-13 21:49               ` Oleksandr
2020-08-13 20:39             ` Oleksandr Tyshchenko
2020-08-13 22:14               ` Julien Grall
2020-08-14 12:08                 ` Oleksandr
2020-08-05 14:12   ` Julien Grall
2020-08-05 14:45     ` Jan Beulich
2020-08-05 19:30     ` Oleksandr
2020-08-06 11:08       ` Julien Grall
2020-08-06 11:29         ` Jan Beulich
2020-08-20 18:30           ` Oleksandr
2020-08-21  6:16             ` Jan Beulich
2020-08-21 11:13               ` Oleksandr
2020-08-06 13:27         ` Oleksandr
2020-08-10 18:25           ` Julien Grall
2020-08-10 19:58             ` Oleksandr
2020-08-05 16:13   ` Jan Beulich
2020-08-05 19:47     ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 05/12] hvm/dm: Introduce xendevicemodel_set_irq_level DM op Oleksandr Tyshchenko
2020-08-04 23:22   ` Stefano Stabellini
2020-08-05  9:39     ` Julien Grall
2020-08-06  0:37       ` Stefano Stabellini
2020-08-06 11:32         ` Julien Grall
2020-08-06 23:49           ` Stefano Stabellini
2020-08-07  8:43             ` Jan Beulich
2020-08-07 21:50               ` Stefano Stabellini
2020-08-08  9:27                 ` Julien Grall
2020-08-08  9:28                   ` Julien Grall
2020-08-10 23:34                   ` Stefano Stabellini
2020-08-11 13:04                     ` Julien Grall
2020-08-11 22:48                       ` Stefano Stabellini
2020-08-18  9:31                         ` Julien Grall
2020-08-21  0:53                           ` Stefano Stabellini
2020-08-17 15:23                 ` Jan Beulich
2020-08-17 22:56                   ` Stefano Stabellini
2020-08-18  8:03                     ` Jan Beulich
2020-08-05 16:15   ` Jan Beulich
2020-08-05 22:12     ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 06/12] libxl: Introduce basic virtio-mmio support on Arm Oleksandr Tyshchenko
2020-08-03 18:21 ` [RFC PATCH V1 07/12] A collection of tweaks to be able to run emulator in driver domain Oleksandr Tyshchenko
2020-08-05 16:19   ` Jan Beulich
2020-08-05 16:40     ` Paul Durrant
2020-08-06  9:22       ` Oleksandr
2020-08-06  9:27         ` Jan Beulich
2020-08-14 16:30           ` Oleksandr
2020-08-16 15:36             ` Julien Grall
2020-08-17 15:07               ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 08/12] xen/arm: Invalidate qemu mapcache on XENMEM_decrease_reservation Oleksandr Tyshchenko
2020-08-05 16:21   ` Jan Beulich
2020-08-06 11:35     ` Julien Grall
2020-08-06 11:50       ` Jan Beulich
2020-08-06 14:28         ` Oleksandr
2020-08-06 16:33           ` Jan Beulich
2020-08-06 16:57             ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 09/12] libxl: Handle virtio-mmio irq in more correct way Oleksandr Tyshchenko
2020-08-04 23:22   ` Stefano Stabellini
2020-08-05 20:51     ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 10/12] libxl: Add support for virtio-disk configuration Oleksandr Tyshchenko
2020-08-04 23:23   ` Stefano Stabellini
2020-08-05 21:12     ` Oleksandr
2020-08-06  0:37       ` Stefano Stabellini
2020-08-03 18:21 ` [RFC PATCH V1 11/12] libxl: Insert "dma-coherent" property into virtio-mmio device node Oleksandr Tyshchenko
2020-08-04 23:23   ` Stefano Stabellini
2020-08-05 20:35     ` Oleksandr
2020-08-03 18:21 ` [RFC PATCH V1 12/12] libxl: Fix duplicate memory node in DT Oleksandr Tyshchenko
2020-08-15 17:24 ` [RFC PATCH V1 00/12] IOREQ feature (+ virtio-mmio) on Arm Julien Grall
2020-08-16 19:34   ` Oleksandr

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