From: Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
To: Jan Beulich <jbeulich@suse.com>,
"roger.pau@citrix.com" <roger.pau@citrix.com>
Cc: "julien@xen.org" <julien@xen.org>,
"sstabellini@kernel.org" <sstabellini@kernel.org>,
Oleksandr Tyshchenko <Oleksandr_Tyshchenko@epam.com>,
Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>,
Artem Mygaiev <Artem_Mygaiev@epam.com>,
"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
"george.dunlap@citrix.com" <george.dunlap@citrix.com>,
"paul@xen.org" <paul@xen.org>,
Bertrand Marquis <bertrand.marquis@arm.com>,
Rahul Singh <rahul.singh@arm.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Oleksandr Andrushchenko <Oleksandr_Andrushchenko@epam.com>
Subject: Re: [PATCH v6 03/13] vpci: move lock outside of struct vpci
Date: Fri, 4 Feb 2022 08:58:19 +0000 [thread overview]
Message-ID: <2cf022f8-b000-11b7-c6b9-90a56bc6e2ea@epam.com> (raw)
In-Reply-To: <7209889d-8f17-61cc-72a4-97f6dbc1d54d@suse.com>
Hi, Jan!
On 04.02.22 09:52, Jan Beulich wrote:
> On 04.02.2022 07:34, Oleksandr Andrushchenko wrote:
>> @@ -285,6 +286,12 @@ static int modify_bars(const struct pci_dev *pdev, uint16_t cmd, bool rom_only)
>> continue;
>> }
>>
>> + spin_lock(&tmp->vpci_lock);
>> + if ( !tmp->vpci )
>> + {
>> + spin_unlock(&tmp->vpci_lock);
>> + continue;
>> + }
>> for ( i = 0; i < ARRAY_SIZE(tmp->vpci->header.bars); i++ )
>> {
>> const struct vpci_bar *bar = &tmp->vpci->header.bars[i];
>> @@ -303,12 +310,14 @@ static int modify_bars(const struct pci_dev *pdev, uint16_t cmd, bool rom_only)
>> rc = rangeset_remove_range(mem, start, end);
>> if ( rc )
>> {
>> + spin_unlock(&tmp->vpci_lock);
>> printk(XENLOG_G_WARNING "Failed to remove [%lx, %lx]: %d\n",
>> start, end, rc);
>> rangeset_destroy(mem);
>> return rc;
>> }
>> }
>> + spin_unlock(&tmp->vpci_lock);
>> }
> At the first glance this simply looks like another unjustified (in the
> description) change, as you're not converting anything here but you
> actually add locking (and I realize this was there before, so I'm sorry
> for not pointing this out earlier).
Well, I thought that the description already has "...the lock can be
used (and in a few cases is used right away) to check whether vpci
is present" and this is enough for such uses as here.
> But then I wonder whether you
> actually tested this, since I can't help getting the impression that
> you're introducing a live-lock: The function is called from cmd_write()
> and rom_write(), which in turn are called out of vpci_write(). Yet that
> function already holds the lock, and the lock is not (currently)
> recursive. (For the 3rd caller of the function - init_bars() - otoh
> the locking looks to be entirely unnecessary.)
Well, you are correct: if tmp != pdev then it is correct to acquire
the lock. But if tmp == pdev and rom_only == true
then we'll deadlock.
It seems we need to have the locking conditional, e.g. only lock
if tmp != pdev
>
> Then again this was present already even in Roger's original patch, so
> I guess I must be missing something ...
>
>> --- a/xen/drivers/vpci/msix.c
>> +++ b/xen/drivers/vpci/msix.c
>> @@ -138,7 +138,7 @@ static void control_write(const struct pci_dev *pdev, unsigned int reg,
>> pci_conf_write16(pdev->sbdf, reg, val);
>> }
>>
>> -static struct vpci_msix *msix_find(const struct domain *d, unsigned long addr)
>> +static struct vpci_msix *msix_get(const struct domain *d, unsigned long addr)
>> {
>> struct vpci_msix *msix;
>>
>> @@ -150,15 +150,29 @@ static struct vpci_msix *msix_find(const struct domain *d, unsigned long addr)
>> for ( i = 0; i < ARRAY_SIZE(msix->tables); i++ )
>> if ( bars[msix->tables[i] & PCI_MSIX_BIRMASK].enabled &&
>> VMSIX_ADDR_IN_RANGE(addr, msix->pdev->vpci, i) )
>> + {
>> + spin_lock(&msix->pdev->vpci_lock);
>> return msix;
>> + }
> I think deliberately returning with a lock held requires a respective
> comment ahead of the function.
Ok, will add a comment
>
>> }
>>
>> return NULL;
>> }
>>
>> +static void msix_put(struct vpci_msix *msix)
>> +{
>> + if ( !msix )
>> + return;
>> +
>> + spin_unlock(&msix->pdev->vpci_lock);
>> +}
> Maybe shorter
>
> if ( msix )
> spin_unlock(&msix->pdev->vpci_lock);
Looks good
>
> ? Yet there's only one case where you may pass NULL in here, so
> maybe it's better anyway to move the conditional ...
>
>> static int msix_accept(struct vcpu *v, unsigned long addr)
>> {
>> - return !!msix_find(v->domain, addr);
>> + struct vpci_msix *msix = msix_get(v->domain, addr);
>> +
>> + msix_put(msix);
>> + return !!msix;
>> }
> ... here?
Yes, I can have that check here, but what if there is yet
another caller of the same? I am not sure whether it is better
to have the check in msix_get or at the caller site.
At the moment (with a single place with NULL possible) I can
move the check. @Roger?
>
>> @@ -186,7 +200,7 @@ static int msix_read(struct vcpu *v, unsigned long addr, unsigned int len,
>> unsigned long *data)
>> {
>> const struct domain *d = v->domain;
>> - struct vpci_msix *msix = msix_find(d, addr);
>> + struct vpci_msix *msix = msix_get(d, addr);
>> const struct vpci_msix_entry *entry;
>> unsigned int offset;
>>
>> @@ -196,7 +210,10 @@ static int msix_read(struct vcpu *v, unsigned long addr, unsigned int len,
>> return X86EMUL_RETRY;
>>
>> if ( !access_allowed(msix->pdev, addr, len) )
>> + {
>> + msix_put(msix);
>> return X86EMUL_OKAY;
>> + }
>>
>> if ( VMSIX_ADDR_IN_RANGE(addr, msix->pdev->vpci, VPCI_MSIX_PBA) )
>> {
>> @@ -222,10 +239,10 @@ static int msix_read(struct vcpu *v, unsigned long addr, unsigned int len,
>> break;
>> }
>>
>> + msix_put(msix);
>> return X86EMUL_OKAY;
>> }
>>
>> - spin_lock(&msix->pdev->vpci->lock);
>> entry = get_entry(msix, addr);
>> offset = addr & (PCI_MSIX_ENTRY_SIZE - 1);
> You're increasing the locked region quite a bit here. If this is really
> needed, it wants explaining. And if this is deemed acceptable as a
> "side effect", it wants justifying or at least stating imo. Same for
> msix_write() then, obviously.
Yes, I do increase the locking region here, but the msix variable needs
to be protected all the time, so it seems to be obvious that it remains
under the lock
> (I'm not sure Roger actually implied this
> when suggesting to switch to the get/put pair.)
>
>> @@ -327,7 +334,12 @@ uint32_t vpci_read(pci_sbdf_t sbdf, unsigned int reg, unsigned int size)
>> if ( !pdev )
>> return vpci_read_hw(sbdf, reg, size);
>>
>> - spin_lock(&pdev->vpci->lock);
>> + spin_lock(&pdev->vpci_lock);
>> + if ( !pdev->vpci )
>> + {
>> + spin_unlock(&pdev->vpci_lock);
>> + return vpci_read_hw(sbdf, reg, size);
>> + }
> Didn't you say you would add justification of this part of the change
> (and its vpci_write() counterpart) to the description?
Again, I am referring to the commit message as described above
>
> Jan
>
Thank you,
Oleksandr
next prev parent reply other threads:[~2022-02-04 8:58 UTC|newest]
Thread overview: 138+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 6:34 [PATCH v6 00/13] PCI devices passthrough on Arm, part 3 Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 01/13] xen/pci: arm: add stub for is_memory_hole Oleksandr Andrushchenko
2022-02-04 8:51 ` Julien Grall
2022-02-04 9:01 ` Oleksandr Andrushchenko
2022-02-04 9:41 ` Julien Grall
2022-02-04 9:47 ` Oleksandr Andrushchenko
2022-02-04 9:57 ` Julien Grall
2022-02-04 10:35 ` Oleksandr Andrushchenko
2022-02-04 11:00 ` Julien Grall
2022-02-04 11:25 ` Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 02/13] rangeset: add RANGESETF_no_print flag Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 03/13] vpci: move lock outside of struct vpci Oleksandr Andrushchenko
2022-02-04 7:52 ` Jan Beulich
2022-02-04 8:13 ` Oleksandr Andrushchenko
2022-02-04 8:36 ` Jan Beulich
2022-02-04 8:58 ` Oleksandr Andrushchenko [this message]
2022-02-04 9:15 ` Jan Beulich
2022-02-04 10:12 ` Oleksandr Andrushchenko
2022-02-04 10:49 ` Jan Beulich
2022-02-04 11:13 ` Roger Pau Monné
2022-02-04 11:37 ` Jan Beulich
2022-02-04 12:37 ` Oleksandr Andrushchenko
2022-02-04 12:47 ` Jan Beulich
2022-02-04 12:53 ` Oleksandr Andrushchenko
2022-02-04 13:03 ` Jan Beulich
2022-02-04 13:06 ` Roger Pau Monné
2022-02-04 14:43 ` Oleksandr Andrushchenko
2022-02-04 14:57 ` Roger Pau Monné
2022-02-07 11:08 ` Oleksandr Andrushchenko
2022-02-07 12:34 ` Jan Beulich
2022-02-07 12:57 ` Oleksandr Andrushchenko
2022-02-07 13:02 ` Jan Beulich
2022-02-07 12:46 ` Roger Pau Monné
2022-02-07 13:53 ` Oleksandr Andrushchenko
2022-02-07 14:11 ` Jan Beulich
2022-02-07 14:27 ` Roger Pau Monné
2022-02-07 14:33 ` Jan Beulich
2022-02-07 14:35 ` Oleksandr Andrushchenko
2022-02-07 15:11 ` Oleksandr Andrushchenko
2022-02-07 15:26 ` Jan Beulich
2022-02-07 16:07 ` Oleksandr Andrushchenko
2022-02-07 16:15 ` Jan Beulich
2022-02-07 16:21 ` Oleksandr Andrushchenko
2022-02-07 16:37 ` Jan Beulich
2022-02-07 16:44 ` Oleksandr Andrushchenko
2022-02-08 7:35 ` Oleksandr Andrushchenko
2022-02-08 8:57 ` Jan Beulich
2022-02-08 9:03 ` Oleksandr Andrushchenko
2022-02-08 10:50 ` Roger Pau Monné
2022-02-08 11:13 ` Oleksandr Andrushchenko
2022-02-08 13:38 ` Roger Pau Monné
2022-02-08 13:52 ` Oleksandr Andrushchenko
2022-02-08 8:53 ` Jan Beulich
2022-02-08 9:00 ` Oleksandr Andrushchenko
2022-02-08 10:11 ` Roger Pau Monné
2022-02-08 10:32 ` Oleksandr Andrushchenko
2022-02-07 16:08 ` Roger Pau Monné
2022-02-07 16:12 ` Jan Beulich
2022-02-07 14:28 ` Oleksandr Andrushchenko
2022-02-07 14:19 ` Roger Pau Monné
2022-02-07 14:27 ` Oleksandr Andrushchenko
2022-02-04 11:37 ` Oleksandr Andrushchenko
2022-02-04 12:15 ` Roger Pau Monné
2022-02-04 10:57 ` Roger Pau Monné
2022-02-04 6:34 ` [PATCH v6 04/13] vpci: restrict unhandled read/write operations for guests Oleksandr Andrushchenko
2022-02-04 14:11 ` Jan Beulich
2022-02-04 14:24 ` Oleksandr Andrushchenko
2022-02-08 8:00 ` Oleksandr Andrushchenko
2022-02-08 9:04 ` Jan Beulich
2022-02-08 9:09 ` Oleksandr Andrushchenko
2022-02-08 9:05 ` Roger Pau Monné
2022-02-08 9:10 ` Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 05/13] vpci: add hooks for PCI device assign/de-assign Oleksandr Andrushchenko
2022-02-07 16:28 ` Jan Beulich
2022-02-08 8:32 ` Oleksandr Andrushchenko
2022-02-08 9:13 ` Jan Beulich
2022-02-08 9:27 ` Oleksandr Andrushchenko
2022-02-08 9:44 ` Jan Beulich
2022-02-08 9:55 ` Oleksandr Andrushchenko
2022-02-08 10:09 ` Jan Beulich
2022-02-08 10:22 ` Oleksandr Andrushchenko
2022-02-08 10:29 ` Jan Beulich
2022-02-08 10:52 ` Oleksandr Andrushchenko
2022-02-08 11:00 ` Jan Beulich
2022-02-08 11:25 ` Oleksandr Andrushchenko
2022-02-10 8:21 ` Oleksandr Andrushchenko
2022-02-10 9:22 ` Jan Beulich
2022-02-10 9:33 ` Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 06/13] vpci/header: implement guest BAR register handlers Oleksandr Andrushchenko
2022-02-07 17:06 ` Jan Beulich
2022-02-08 8:06 ` Oleksandr Andrushchenko
2022-02-08 9:16 ` Jan Beulich
2022-02-08 9:29 ` Roger Pau Monné
2022-02-08 9:25 ` Roger Pau Monné
2022-02-08 9:31 ` Oleksandr Andrushchenko
2022-02-08 9:48 ` Jan Beulich
2022-02-08 9:57 ` Oleksandr Andrushchenko
2022-02-08 10:15 ` Jan Beulich
2022-02-08 10:29 ` Oleksandr Andrushchenko
2022-02-08 13:58 ` Roger Pau Monné
2022-02-04 6:34 ` [PATCH v6 07/13] vpci/header: handle p2m range sets per BAR Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 08/13] vpci/header: program p2m with guest BAR view Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 09/13] vpci/header: emulate PCI_COMMAND register for guests Oleksandr Andrushchenko
2022-02-04 14:25 ` Jan Beulich
2022-02-08 8:13 ` Oleksandr Andrushchenko
2022-02-08 9:33 ` Jan Beulich
2022-02-08 9:38 ` Oleksandr Andrushchenko
2022-02-08 9:52 ` Jan Beulich
2022-02-08 9:58 ` Oleksandr Andrushchenko
2022-02-08 11:11 ` Roger Pau Monné
2022-02-08 11:29 ` Oleksandr Andrushchenko
2022-02-08 14:09 ` Roger Pau Monné
2022-02-08 14:13 ` Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 10/13] vpci/header: reset the command register when adding devices Oleksandr Andrushchenko
2022-02-04 14:30 ` Jan Beulich
2022-02-04 14:37 ` Oleksandr Andrushchenko
2022-02-07 7:29 ` Jan Beulich
2022-02-07 11:27 ` Oleksandr Andrushchenko
2022-02-07 12:38 ` Jan Beulich
2022-02-07 12:51 ` Oleksandr Andrushchenko
2022-02-07 12:54 ` Jan Beulich
2022-02-07 14:17 ` Oleksandr Andrushchenko
2022-02-07 14:31 ` Jan Beulich
2022-02-07 14:46 ` Oleksandr Andrushchenko
2022-02-07 15:05 ` Jan Beulich
2022-02-07 15:14 ` Oleksandr Andrushchenko
2022-02-07 15:28 ` Jan Beulich
2022-02-07 15:59 ` Oleksandr Andrushchenko
2022-02-10 12:54 ` Oleksandr Andrushchenko
2022-02-10 13:36 ` Jan Beulich
2022-02-10 13:56 ` Oleksandr Andrushchenko
2022-02-10 12:59 ` Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 11/13] vpci: add initial support for virtual PCI bus topology Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 12/13] xen/arm: translate virtual PCI bus topology for guests Oleksandr Andrushchenko
2022-02-04 7:56 ` Jan Beulich
2022-02-04 8:18 ` Oleksandr Andrushchenko
2022-02-04 6:34 ` [PATCH v6 13/13] xen/arm: account IO handlers for emulated PCI MSI-X Oleksandr Andrushchenko
2022-02-11 15:28 ` Julien Grall
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