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From: Paul Durrant <xadimgnik@gmail.com>
To: "'Jan Beulich'" <jbeulich@suse.com>, "'Oleksandr'" <olekstysh@gmail.com>
Cc: "'Oleksandr Tyshchenko'" <oleksandr_tyshchenko@epam.com>,
	"'Stefano Stabellini'" <sstabellini@kernel.org>,
	"'Julien Grall'" <julien@xen.org>,
	"'Volodymyr Babchuk'" <Volodymyr_Babchuk@epam.com>,
	"'Andrew Cooper'" <andrew.cooper3@citrix.com>,
	"'George Dunlap'" <george.dunlap@citrix.com>,
	"'Ian Jackson'" <iwj@xenproject.org>, "'Wei Liu'" <wl@xen.org>,
	"'Julien Grall'" <julien.grall@arm.com>,
	<xen-devel@lists.xenproject.org>
Subject: RE: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
Date: Wed, 11 Nov 2020 16:28:05 -0000	[thread overview]
Message-ID: <003401d6b847$a2d9f470$e88ddd50$@xen.org> (raw)
In-Reply-To: <0ab03a33-5056-0de8-e5f7-b54a661a09c5@suse.com>

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: 11 November 2020 13:28
> To: Oleksandr <olekstysh@gmail.com>
> Cc: 'Oleksandr Tyshchenko' <oleksandr_tyshchenko@epam.com>; 'Stefano Stabellini'
> <sstabellini@kernel.org>; 'Julien Grall' <julien@xen.org>; 'Volodymyr Babchuk'
> <Volodymyr_Babchuk@epam.com>; 'Andrew Cooper' <andrew.cooper3@citrix.com>; 'George Dunlap'
> <george.dunlap@citrix.com>; 'Ian Jackson' <iwj@xenproject.org>; 'Wei Liu' <wl@xen.org>; 'Julien Grall'
> <julien.grall@arm.com>; paul@xen.org; xen-devel@lists.xenproject.org
> Subject: Re: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
> 
> On 11.11.2020 09:41, Oleksandr wrote:
> >
> > On 11.11.20 10:08, Jan Beulich wrote:
> >
> > Hi Jan
> >
> >> On 10.11.2020 21:53, Oleksandr wrote:
> >>> On 20.10.20 13:51, Paul Durrant wrote:
> >>>
> >>> Hi Paul.
> >>>
> >>> Sorry for the late response.
> >>>
> >>>>> -----Original Message-----
> >>>>> From: Oleksandr Tyshchenko <olekstysh@gmail.com>
> >>>>> Sent: 15 October 2020 17:44
> >>>>> To: xen-devel@lists.xenproject.org
> >>>>> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>; Stefano Stabellini
> <sstabellini@kernel.org>;
> >>>>> Julien Grall <julien@xen.org>; Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>; Andrew Cooper
> >>>>> <andrew.cooper3@citrix.com>; George Dunlap <george.dunlap@citrix.com>; Ian Jackson
> >>>>> <iwj@xenproject.org>; Jan Beulich <jbeulich@suse.com>; Wei Liu <wl@xen.org>; Paul Durrant
> >>>>> <paul@xen.org>; Julien Grall <julien.grall@arm.com>
> >>>>> Subject: [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server()
> >>>>>
> >>>>> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> >>>>>
> >>>>> This patch introduces a helper the main purpose of which is to check
> >>>>> if a domain is using IOREQ server(s).
> >>>>>
> >>>>> On Arm the current benefit is to avoid calling handle_io_completion()
> >>>>> (which implies iterating over all possible IOREQ servers anyway)
> >>>>> on every return in leave_hypervisor_to_guest() if there is no active
> >>>>> servers for the particular domain.
> >>>>> Also this helper will be used by one of the subsequent patches on Arm.
> >>>>>
> >>>>> This involves adding an extra per-domain variable to store the count
> >>>>> of servers in use.
> >>>>>
> >>>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> >>>>> CC: Julien Grall <julien.grall@arm.com>
> >>>>>
> >>>>> ---
> >>>>> Please note, this is a split/cleanup/hardening of Julien's PoC:
> >>>>> "Add support for Guest IO forwarding to a device emulator"
> >>>>>
> >>>>> Changes RFC -> V1:
> >>>>>      - new patch
> >>>>>
> >>>>> Changes V1 -> V2:
> >>>>>      - update patch description
> >>>>>      - guard helper with CONFIG_IOREQ_SERVER
> >>>>>      - remove "hvm" prefix
> >>>>>      - modify helper to just return d->arch.hvm.ioreq_server.nr_servers
> >>>>>      - put suitable ASSERT()s
> >>>>>      - use ASSERT(d->ioreq_server.server[id] ? !s : !!s) in set_ioreq_server()
> >>>>>      - remove d->ioreq_server.nr_servers = 0 from hvm_ioreq_init()
> >>>>> ---
> >>>>>    xen/arch/arm/traps.c    | 15 +++++++++------
> >>>>>    xen/common/ioreq.c      |  7 ++++++-
> >>>>>    xen/include/xen/ioreq.h | 14 ++++++++++++++
> >>>>>    xen/include/xen/sched.h |  1 +
> >>>>>    4 files changed, 30 insertions(+), 7 deletions(-)
> >>>>>
> >>>>> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> >>>>> index 507c095..a8f5fdf 100644
> >>>>> --- a/xen/arch/arm/traps.c
> >>>>> +++ b/xen/arch/arm/traps.c
> >>>>> @@ -2261,14 +2261,17 @@ static bool check_for_vcpu_work(void)
> >>>>>        struct vcpu *v = current;
> >>>>>
> >>>>>    #ifdef CONFIG_IOREQ_SERVER
> >>>>> -    bool handled;
> >>>>> +    if ( domain_has_ioreq_server(v->domain) )
> >>>>> +    {
> >>>>> +        bool handled;
> >>>>>
> >>>>> -    local_irq_enable();
> >>>>> -    handled = handle_io_completion(v);
> >>>>> -    local_irq_disable();
> >>>>> +        local_irq_enable();
> >>>>> +        handled = handle_io_completion(v);
> >>>>> +        local_irq_disable();
> >>>>>
> >>>>> -    if ( !handled )
> >>>>> -        return true;
> >>>>> +        if ( !handled )
> >>>>> +            return true;
> >>>>> +    }
> >>>>>    #endif
> >>>>>
> >>>>>        if ( likely(!v->arch.need_flush_to_ram) )
> >>>>> diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
> >>>>> index bcd4961..a72bc0e 100644
> >>>>> --- a/xen/common/ioreq.c
> >>>>> +++ b/xen/common/ioreq.c
> >>>>> @@ -39,9 +39,14 @@ static void set_ioreq_server(struct domain *d, unsigned int id,
> >>>>>                                 struct ioreq_server *s)
> >>>>>    {
> >>>>>        ASSERT(id < MAX_NR_IOREQ_SERVERS);
> >>>>> -    ASSERT(!s || !d->ioreq_server.server[id]);
> >>>>> +    ASSERT(d->ioreq_server.server[id] ? !s : !!s);
> >>>> That looks odd. How about ASSERT(!s ^ !d->ioreq_server.server[id])?
> >>> ok, looks like it will work.
> >>>
> >>>
> >>>>     Paul
> >>>>
> >>>>>        d->ioreq_server.server[id] = s;
> >>>>> +
> >>>>> +    if ( s )
> >>>>> +        d->ioreq_server.nr_servers++;
> >>>>> +    else
> >>>>> +        d->ioreq_server.nr_servers--;
> >>>>>    }
> >>>>>
> >>>>>    #define GET_IOREQ_SERVER(d, id) \
> >>>>> diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
> >>>>> index 7b03ab5..0679fef 100644
> >>>>> --- a/xen/include/xen/ioreq.h
> >>>>> +++ b/xen/include/xen/ioreq.h
> >>>>> @@ -55,6 +55,20 @@ struct ioreq_server {
> >>>>>        uint8_t                bufioreq_handling;
> >>>>>    };
> >>>>>
> >>>>> +#ifdef CONFIG_IOREQ_SERVER
> >>>>> +static inline bool domain_has_ioreq_server(const struct domain *d)
> >>>>> +{
> >>>>> +    ASSERT((current->domain == d) || atomic_read(&d->pause_count));
> >>>>> +
> >>>> This seems like an odd place to put such an assertion.
> >>> I might miss something or interpreted incorrectly but these asserts are
> >>> the result of how I understood the review comment on previous version [1].
> >>>
> >>> I will copy a comment here for the convenience:
> >>> "This is safe only when d == current->domain and it's not paused,
> >>> or when they're distinct and d is paused. Otherwise the result is
> >>> stale before the caller can inspect it. This wants documenting by
> >>> at least a comment, but perhaps better by suitable ASSERT()s."
> >> The way his reply was worded, I think Paul was wondering about the
> >> place where you put the assertion, not what you actually assert.
> >
> > Shall I put the assertion at the call sites of this helper instead?
> 
> Since Paul raised the question, I expect this is a question to him
> rather than me?

If it is indeed a question for me then yes, put the assertion where it is clear why it is needed. domain_has_ioreq_server() is essentially a trivial accessor function; it's not the appropriate place.

  Paul

> 
> Jan



  reply	other threads:[~2020-11-11 16:28 UTC|newest]

Thread overview: 109+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-15 16:44 [PATCH V2 00/23] IOREQ feature (+ virtio-mmio) on Arm Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 01/23] x86/ioreq: Prepare IOREQ feature for making it common Oleksandr Tyshchenko
2020-10-20  7:13   ` Paul Durrant
2020-11-04  9:06     ` Oleksandr
2020-11-04  9:59       ` Paul Durrant
2020-11-12 10:58   ` Jan Beulich
2020-11-13 11:09     ` Oleksandr
2020-11-13 11:20       ` Jan Beulich
2020-11-13 12:45         ` Oleksandr
2020-11-13 14:31           ` Jan Beulich
2020-10-15 16:44 ` [PATCH V2 02/23] xen/ioreq: Make x86's IOREQ feature common Oleksandr Tyshchenko
2020-10-20  7:57   ` Paul Durrant
2020-11-10 16:45     ` Oleksandr
2020-11-17 14:47       ` Oleksandr
2020-11-17 15:29         ` Paul Durrant
2020-11-17 16:29           ` Oleksandr
2020-11-17 19:43             ` Paul Durrant
2020-11-12 11:11   ` Jan Beulich
2020-11-13 13:11     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 03/23] xen/ioreq: Make x86's hvm_ioreq_needs_completion() common Oleksandr Tyshchenko
2020-10-20  7:59   ` Paul Durrant
2020-10-15 16:44 ` [PATCH V2 04/23] xen/ioreq: Provide alias for the handle_mmio() Oleksandr Tyshchenko
2020-10-20  9:14   ` Paul Durrant
2020-10-20 10:05     ` Jan Beulich
2020-10-20 10:38       ` Paul Durrant
2020-11-10 19:44         ` Oleksandr
2020-11-11  7:27           ` Jan Beulich
2020-11-11  8:09             ` Oleksandr
2020-11-11  8:16               ` Jan Beulich
2020-10-15 16:44 ` [PATCH V2 05/23] xen/ioreq: Make x86's hvm_mmio_first(last)_byte() common Oleksandr Tyshchenko
2020-10-20  9:15   ` Paul Durrant
2020-10-15 16:44 ` [PATCH V2 06/23] xen/ioreq: Make x86's hvm_ioreq_(page/vcpu/server) structs common Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 07/23] xen/ioreq: Move x86's ioreq_gfn(server) to struct domain Oleksandr Tyshchenko
2020-11-12 11:21   ` Jan Beulich
2020-11-13 14:05     ` Oleksandr
2020-11-18 12:09   ` Oleksandr
2020-11-18 12:29     ` Paul Durrant
2020-10-15 16:44 ` [PATCH V2 08/23] xen/ioreq: Introduce ioreq_params to abstract accesses to arch.hvm.params Oleksandr Tyshchenko
2020-10-20 10:41   ` Paul Durrant
2020-11-10 20:00     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 09/23] xen/dm: Make x86's DM feature common Oleksandr Tyshchenko
2020-11-12 11:32   ` Jan Beulich
2020-11-13 14:28     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 10/23] xen/mm: Make x86's XENMEM_resource_ioreq_server handling common Oleksandr Tyshchenko
2020-11-12 11:40   ` Jan Beulich
2020-11-13 15:00     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 11/23] xen/ioreq: Move x86's io_completion/io_req fields to struct vcpu Oleksandr Tyshchenko
2020-10-20 10:55   ` Paul Durrant
2020-11-10 20:59     ` Oleksandr
2020-11-11  8:04   ` Jan Beulich
2020-11-11  8:14     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 12/23] xen/ioreq: Remove "hvm" prefixes from involved function names Oleksandr Tyshchenko
2020-11-12 11:45   ` Jan Beulich
2020-11-12 12:14     ` Paul Durrant
2020-11-13 15:53     ` Oleksandr
2020-11-23 14:39       ` Oleksandr
2020-11-23 14:56         ` Jan Beulich
2020-11-23 15:47           ` Oleksandr
2020-11-23 15:54             ` Paul Durrant
2020-11-23 16:36               ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 13/23] xen/ioreq: Use guest_cmpxchg64() instead of cmpxchg() Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 14/23] arm/ioreq: Introduce arch specific bits for IOREQ/DM features Oleksandr Tyshchenko
2020-11-12 11:48   ` Jan Beulich
2020-11-13 15:48     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 15/23] xen/arm: Stick around in leave_hypervisor_to_guest until I/O has completed Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 16/23] xen/mm: Handle properly reference in set_foreign_p2m_entry() on Arm Oleksandr Tyshchenko
2020-11-12 12:18   ` Jan Beulich
2020-11-13 17:00     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 17/23] xen/ioreq: Introduce domain_has_ioreq_server() Oleksandr Tyshchenko
2020-10-20 10:51   ` Paul Durrant
2020-11-10 20:53     ` Oleksandr
2020-11-11  8:08       ` Jan Beulich
2020-11-11  8:41         ` Oleksandr
2020-11-11 13:27           ` Jan Beulich
2020-11-11 16:28             ` Paul Durrant [this message]
2020-11-11 17:33               ` Oleksandr
2020-11-11 17:31             ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 18/23] xen/dm: Introduce xendevicemodel_set_irq_level DM op Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 19/23] xen/arm: io: Abstract sign-extension Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 20/23] xen/ioreq: Make x86's send_invalidate_req() common Oleksandr Tyshchenko
2020-11-12 11:55   ` Jan Beulich
2020-11-13 16:03     ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 21/23] xen/arm: Add mapcache invalidation handling Oleksandr Tyshchenko
2020-10-16  6:29   ` Jan Beulich
2020-10-16  8:41     ` Julien Grall
2020-10-16  8:56       ` Jan Beulich
2020-11-11  0:03       ` Oleksandr
2020-11-11 19:27         ` Julien Grall
2020-11-11 19:42           ` Oleksandr
2020-10-15 16:44 ` [PATCH V2 22/23] libxl: Introduce basic virtio-mmio support on Arm Oleksandr Tyshchenko
2020-10-15 16:44 ` [PATCH V2 23/23] [RFC] libxl: Add support for virtio-disk configuration Oleksandr Tyshchenko
2020-11-09  6:45   ` Wei Chen
2020-11-11  0:53     ` Oleksandr
2020-11-11  4:28       ` Wei Chen
2020-11-13 17:38         ` Oleksandr
2020-10-29  7:41 ` [PATCH V2 00/23] IOREQ feature (+ virtio-mmio) on Arm Masami Hiramatsu
2020-10-29 18:48   ` Oleksandr Tyshchenko
2020-10-29 19:53     ` Stefano Stabellini
2020-10-29 21:13       ` Oleksandr Tyshchenko
2020-10-29 21:34         ` Stefano Stabellini
2020-10-30 11:34         ` Masami Hiramatsu
2020-10-31 21:10           ` Oleksandr Tyshchenko
2020-11-02  7:23             ` Wei Chen
2020-11-02 18:05               ` Oleksandr
2020-11-03 14:30             ` Masami Hiramatsu
2020-11-03 21:09               ` Oleksandr
2020-10-29 20:03     ` Alex Bennée
2020-10-29 20:10       ` Stefano Stabellini
2020-10-29 22:06       ` Oleksandr Tyshchenko

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