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r32mr2472002pgb.393.1559274973315; Thu, 30 May 2019 20:56:13 -0700 (PDT) Received: from [10.61.2.175] ([122.99.82.10]) by smtp.gmail.com with ESMTPSA id s66sm3940582pgs.87.2019.05.30.20.56.09 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 30 May 2019 20:56:12 -0700 (PDT) Subject: Re: [PATCH v3 1/3] PCI: Introduce pcibios_ignore_alignment_request To: Shawn Anastasio , Oliver Cc: Sam Bobroff , linux-pci@vger.kernel.org, Linux Kernel Mailing List , rppt@linux.ibm.com, Paul Mackerras , Bjorn Helgaas , xyjxie@linux.vnet.ibm.com, linuxppc-dev References: <20190528040313.35582-1-shawn@anastas.io> <20190528040313.35582-2-shawn@anastas.io> <3e6b9d7d-5d18-645e-5ef9-6b8a77fa62e9@ozlabs.ru> <985681e4-1236-fff7-e9e7-189a340487dd@anastas.io> From: Alexey Kardashevskiy Openpgp: preference=signencrypt Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD 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ikTJSxWUKmh7OP5mrqhwNe0ezgGiWxxvyNwThOHc5JvpzJLd32VDFilbxgu4Hhnf6LcgZJ2c Zd44XWqUu7FzVOYaSgIvTP0hNrBYm/E6M7yrLbs3JY74fGzPWGRbBUHTZXQEqQnZglXaVB5V ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: <81a015ed-2c99-7ca8-c5ad-cede93aeba97@ozlabs.ru> Date: Fri, 31 May 2019 13:56:07 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <985681e4-1236-fff7-e9e7-189a340487dd@anastas.io> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On 31/05/2019 08:49, Shawn Anastasio wrote: > On 5/29/19 10:39 PM, Alexey Kardashevskiy wrote: >> >> >> On 28/05/2019 17:39, Shawn Anastasio wrote: >>> >>> >>> On 5/28/19 1:27 AM, Alexey Kardashevskiy wrote: >>>> >>>> >>>> On 28/05/2019 15:36, Oliver wrote: >>>>> On Tue, May 28, 2019 at 2:03 PM Shawn Anastasio >>>>> wrote: >>>>>> >>>>>> Introduce a new pcibios function pcibios_ignore_alignment_request >>>>>> which allows the PCI core to defer to platform-specific code to >>>>>> determine whether or not to ignore alignment requests for PCI >>>>>> resources. >>>>>> >>>>>> The existing behavior is to simply ignore alignment requests when >>>>>> PCI_PROBE_ONLY is set. This is behavior is maintained by the >>>>>> default implementation of pcibios_ignore_alignment_request. >>>>>> >>>>>> Signed-off-by: Shawn Anastasio >>>>>> --- >>>>>>    drivers/pci/pci.c   | 9 +++++++-- >>>>>>    include/linux/pci.h | 1 + >>>>>>    2 files changed, 8 insertions(+), 2 deletions(-) >>>>>> >>>>>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c >>>>>> index 8abc843b1615..8207a09085d1 100644 >>>>>> --- a/drivers/pci/pci.c >>>>>> +++ b/drivers/pci/pci.c >>>>>> @@ -5882,6 +5882,11 @@ resource_size_t __weak >>>>>> pcibios_default_alignment(void) >>>>>>           return 0; >>>>>>    } >>>>>> >>>>>> +int __weak pcibios_ignore_alignment_request(void) >>>>>> +{ >>>>>> +       return pci_has_flag(PCI_PROBE_ONLY); >>>>>> +} >>>>>> + >>>>>>    #define RESOURCE_ALIGNMENT_PARAM_SIZE COMMAND_LINE_SIZE >>>>>>    static char >>>>>> resource_alignment_param[RESOURCE_ALIGNMENT_PARAM_SIZE] = {0}; >>>>>>    static DEFINE_SPINLOCK(resource_alignment_lock); >>>>>> @@ -5906,9 +5911,9 @@ static resource_size_t >>>>>> pci_specified_resource_alignment(struct pci_dev *dev, >>>>>>           p = resource_alignment_param; >>>>>>           if (!*p && !align) >>>>>>                   goto out; >>>>>> -       if (pci_has_flag(PCI_PROBE_ONLY)) { >>>>>> +       if (pcibios_ignore_alignment_request()) { >>>>>>                   align = 0; >>>>>> -               pr_info_once("PCI: Ignoring requested alignments >>>>>> (PCI_PROBE_ONLY)\n"); >>>>>> +               pr_info_once("PCI: Ignoring requested alignments\n"); >>>>>>                   goto out; >>>>>>           } >>>>> >>>>> I think the logic here is questionable to begin with. If the user has >>>>> explicitly requested re-aligning a resource via the command line then >>>>> we should probably do it even if PCI_PROBE_ONLY is set. When it breaks >>>>> they get to keep the pieces. >>>>> >>>>> That said, the real issue here is that PCI_PROBE_ONLY probably >>>>> shouldn't be set under qemu/kvm. Under the other hypervisor (PowerVM) >>>>> hotplugged devices are configured by firmware before it's passed to >>>>> the guest and we need to keep the FW assignments otherwise things >>>>> break. QEMU however doesn't do any BAR assignments and relies on that >>>>> being handled by the guest. At boot time this is done by SLOF, but >>>>> Linux only keeps SLOF around until it's extracted the device-tree. >>>>> Once that's done SLOF gets blown away and the kernel needs to do it's >>>>> own BAR assignments. I'm guessing there's a hack in there to make it >>>>> work today, but it's a little surprising that it works at all... >>>> >>>> >>>> The hack is to run a modified qemu-aware "/usr/sbin/rtas_errd" in the >>>> guest which receives an event from qemu (RAS_EPOW from >>>> /proc/interrupts), fetches device tree chunks (and as I understand it - >>>> they come with BARs from phyp but without from qemu) and writes "1" to >>>> "/sys/bus/pci/rescan" which calls pci_assign_resource() eventually: >>> >>> Interesting. Does this mean that the PHYP hotplug path doesn't >>> call pci_assign_resource? >> >> >> I'd expect dlpar_add_slot() to be called under phyp and eventually >> pci_device_add() which (I think) may or may not trigger later >> reassignment. >> >> >>> If so it means the patch may not >>> break that platform after all, though it still may not be >>> the correct way of doing things. >> >> >> We should probably stop enforcing the PCI_PROBE_ONLY flag - it seems >> that (unless resource_alignment= is used) the pseries guest should just >> walk through all allocated resources and leave them unchanged. > > If we add a pcibios_default_alignment() implementation like was > suggested earlier, then it will behave as if the user has > specified resource_alignment= by default and SLOF's assignments > won't be honored (I think). I removed pci_add_flags(PCI_PROBE_ONLY) from pSeries_setup_arch and tried booting with and without pci=resource_alignment= and I can see no difference - BARs are still aligned to 64K as programmed in SLOF; if I hack SLOF to align to 4K or 32K - BARs get packed and the guest leaves them unchanged. > I guess it boils down to one question - is it important that we > observe SLOF's initial BAR assignments? It isn't if it's SLOF but it is if it's phyp. It used to not allow/support BAR reassignment and even if it does not, I'd rather avoid touching them. > If not, the device tree > modification that Sam found would work fine here. Otherwise, > we need a way to honor the initial assignments from SLOF while > still allowing custom alignments for hotplugged devices, either > by deferring to the platform code like I do here, unsetting > PCI_PROBE_ONLY in certain cases or by using IORESOURCE_PCI_FIXED > like Bjorn suggested. > >> >> >>>> [c000000006e6f960] [c0000000005f62d4] pci_assign_resource+0x44/0x360 >>>> >>>> [c000000006e6fa10] [c0000000005f8b54] >>>> assign_requested_resources_sorted+0x84/0x110 >>>> [c000000006e6fa60] [c0000000005f9540] >>>> __assign_resources_sorted+0xd0/0x750 >>>> [c000000006e6fb40] [c0000000005fb2e0] >>>> __pci_bus_assign_resources+0x80/0x280 >>>> [c000000006e6fc00] [c0000000005fb95c] >>>> pci_assign_unassigned_bus_resources+0xbc/0x100 >>>> [c000000006e6fc60] [c0000000005e3d74] pci_rescan_bus+0x34/0x60 >>>> >>>> [c000000006e6fc90] [c0000000005f1ef4] rescan_store+0x84/0xc0 >>>> >>>> [c000000006e6fcd0] [c00000000068060c] bus_attr_store+0x3c/0x60 >>>> >>>> [c000000006e6fcf0] [c00000000037853c] sysfs_kf_write+0x5c/0x80 >>>> >>>> >>>> >>>> >>>> >>>>> >>>>> IIRC Sam Bobroff was looking at hotplug under pseries recently so he >>>>> might have something to add. He's sick at the moment, but I'll ask him >>>>> to take a look at this once he's back among the living >>>>> >>>>>> diff --git a/include/linux/pci.h b/include/linux/pci.h >>>>>> index 4a5a84d7bdd4..47471dcdbaf9 100644 >>>>>> --- a/include/linux/pci.h >>>>>> +++ b/include/linux/pci.h >>>>>> @@ -1990,6 +1990,7 @@ static inline void >>>>>> pcibios_penalize_isa_irq(int irq, int active) {} >>>>>>    int pcibios_alloc_irq(struct pci_dev *dev); >>>>>>    void pcibios_free_irq(struct pci_dev *dev); >>>>>>    resource_size_t pcibios_default_alignment(void); >>>>>> +int pcibios_ignore_alignment_request(void); >>>>>> >>>>>>    #ifdef CONFIG_HIBERNATE_CALLBACKS >>>>>>    extern struct dev_pm_ops pcibios_pm_ops; >>>>>> --  >>>>>> 2.20.1 >>>>>> >>>> >> -- Alexey