From: "Jan Beulich" <JBeulich@suse.com>
To: Paul Durrant <Paul.Durrant@citrix.com>
Cc: Andrew Cooper <Andrew.Cooper3@citrix.com>,
"Keir(Xen.org)" <keir@xen.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v2 01/17] x86/hvm: simplify hvmemul_do_io()
Date: Wed, 17 Jun 2015 15:47:45 +0100 [thread overview]
Message-ID: <5581A4B102000078000863F4@mail.emea.novell.com> (raw)
In-Reply-To: <9AAE0902D5BC7E449B7C8E4E778ABCD0259531E4@AMSPEX01CL01.citrite.net>
>>> On 17.06.15 at 15:54, <Paul.Durrant@citrix.com> wrote:
>> -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@suse.com]
>> Sent: 17 June 2015 14:31
>> >>> On 11.06.15 at 17:42, <paul.durrant@citrix.com> wrote:
>> > @@ -190,7 +141,12 @@ static int hvmemul_do_io(
>> > p.count = *reps;
>> >
>> > if ( dir == IOREQ_WRITE )
>> > + {
>> > + if ( !data_is_addr )
>> > + memcpy(&p.data, p_data, size);
>> > +
>> > hvmtrace_io_assist(is_mmio, &p);
>> > + }
>>
>> Why would you need to do this _only_ here (i.e. either not at all,
>> or not just for tracing purposes)? Or is this just to _restore_ the
>> original value for tracing (in which case the question would be
>> whether it indeed can get modified)?
>
> Not sure I follow. If hvmemul_do_io is called with !data_is_addr then the
> data arg will be a pointer to a buffer, rather than a gpa. So, the gpa that
> was first copied into the ioreq (i.e. p) needs to be overwritten with the
> actual data if it's a write.
Ah, it's being moved here from about 100 lines up (in the original
code) - I simply forgot about that deletion by the time I got here.
>> > +static void hvmemul_release_page(struct page_info *page)
>>
>> inline?
>>
>
> Probably, but I was hoping the compiler would make that decision.
Likely it will, but for functions as simple as this one we can help it.
>> > +/*
>> > + * Perform I/O between <port> and <buffer>. <dir> indicates the
>> > + * direction: IOREQ_READ means a read from <port> to <buffer> and
>> > + * IOREQ_WRITE means a write from <buffer> to <port>. Each access has
>> > + * width <size> and up to *<reps> accesses will be performed. If
>> > + * X86EMUL_OKAY is returned then <reps> will be updated with the
>> number
>> > + * of accesses actually performed.
>> > + *
>> > + * NOTE: If *<reps> is greater than 1, each access will use the
>> > + * <buffer> pointer; there is no implicit interation over a
>> > + * block of memory starting at <buffer>.
>> > + */
>> > +int hvmemul_do_pio_buffer(uint16_t port,
>> > + unsigned long *reps,
>>
>> Considering the comment - can't you instead drop the reps parameter
>> here then?
>>
>
> No. A rep stos does multiple port writes from the same buffer pointer.
A REP STOS doesn't do any port writes at all. REP OUTS does, but
it accesses "a block of memory", which the comment specifically says
doesn't happen here. I.e. I still think either the comment is wrong (or
at least misleading) or the function could be simplified.
Jan
next prev parent reply other threads:[~2015-06-17 14:47 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-11 15:42 [PATCH v2 00/17] x86/hvm: I/O emulation cleanup and fix Paul Durrant
2015-06-11 15:42 ` [PATCH v2 01/17] x86/hvm: simplify hvmemul_do_io() Paul Durrant
2015-06-17 13:31 ` Jan Beulich
2015-06-17 13:54 ` Paul Durrant
2015-06-17 14:47 ` Jan Beulich [this message]
2015-06-17 14:55 ` Paul Durrant
2015-06-17 14:59 ` Jan Beulich
2015-06-11 15:42 ` [PATCH v2 02/17] x86/hvm: re-name struct hvm_mmio_handler to hvm_mmio_ops Paul Durrant
2015-06-17 12:43 ` Jan Beulich
2015-06-17 12:45 ` Paul Durrant
2015-06-11 15:42 ` [PATCH v2 03/17] x86/hvm: unify internal portio and mmio intercepts Paul Durrant
2015-06-17 14:22 ` Jan Beulich
2015-06-17 14:40 ` Paul Durrant
2015-06-17 14:55 ` Jan Beulich
2015-06-11 15:42 ` [PATCH v2 04/17] x86/hvm: unify dpci portio intercept with standard portio intercept Paul Durrant
2015-06-17 14:36 ` Jan Beulich
2015-06-17 14:46 ` Paul Durrant
2015-06-17 14:58 ` Jan Beulich
2015-06-17 15:17 ` Paul Durrant
2015-06-11 15:42 ` [PATCH v2 05/17] x86/hvm: unify stdvga mmio intercept with standard mmio intercept Paul Durrant
2015-06-17 15:50 ` Jan Beulich
2015-06-17 16:30 ` Paul Durrant
2015-06-18 6:23 ` Jan Beulich
2015-06-11 15:42 ` [PATCH v2 06/17] x86/hvm: revert 82ed8716b "fix direct PCI port I/O emulation retry Paul Durrant
2015-06-17 10:54 ` Paul Durrant
2015-06-11 15:42 ` [PATCH v2 07/17] x86/hvm: only call hvm_io_assist() from hvm_wait_for_io() Paul Durrant
2015-06-11 15:42 ` [PATCH v2 08/17] x86/hvm: split I/O completion handling from state model Paul Durrant
2015-06-11 15:42 ` [PATCH v2 09/17] x86/hvm: remove hvm_io_pending() check in hvmemul_do_io() Paul Durrant
2015-06-11 15:42 ` [PATCH v2 10/17] x86/hvm: remove HVMIO_dispatched I/O state Paul Durrant
2015-06-11 15:42 ` [PATCH v2 11/17] x86/hvm: remove hvm_io_state enumeration Paul Durrant
2015-06-11 15:42 ` [PATCH v2 12/17] x86/hvm: use ioreq_t to track in-flight state Paul Durrant
2015-06-11 15:42 ` [PATCH v2 13/17] x86/hvm: only acquire RAM pages for emulation when we need to Paul Durrant
2015-06-11 15:42 ` [PATCH v2 14/17] x86/hvm: remove extraneous parameter from hvmtrace_io_assist() Paul Durrant
2015-06-11 15:42 ` [PATCH v2 15/17] x86/hvm: make sure translated MMIO reads or writes fall within a page Paul Durrant
2015-06-11 15:43 ` [PATCH v2 16/17] x86/hvm: remove multiple open coded 'chunking' loops Paul Durrant
2015-06-11 15:43 ` [PATCH v2 17/17] x86/hvm: track large memory mapped accesses by buffer offset Paul Durrant
2015-06-12 10:44 ` [PATCH v2 00/17] x86/hvm: I/O emulation cleanup and fix Fabio Fantoni
2015-06-12 11:45 ` Paul Durrant
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