From: "H. Peter Anvin" <hpa@zytor.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, Ajay Kaher <akaher@vmware.com>
Cc: "x86@kernel.org" <x86@kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"rostedt@goodmis.org" <rostedt@goodmis.org>,
Srivatsa Bhat <srivatsab@vmware.com>,
"srivatsa@csail.mit.edu" <srivatsa@csail.mit.edu>,
Alexey Makhalov <amakhalov@vmware.com>,
Vasavi Sirnapalli <vsirnapalli@vmware.com>,
"er.ajay.kaher@gmail.com" <er.ajay.kaher@gmail.com>,
"willy@infradead.org" <willy@infradead.org>,
Nadav Amit <namit@vmware.com>,
"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"jailhouse-dev@googlegroups.com" <jailhouse-dev@googlegroups.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
"acrn-dev@lists.projectacrn.org" <acrn-dev@lists.projectacrn.org>,
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"bhelgaas@google.com" <bhelgaas@google.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"mingo@redhat.com" <mingo@redhat.com>,
"bp@alien8.de" <bp@alien8.de>,
"dave.hansen@linux.intel.com" <dave.hansen@linux.intel.com>,
Alexander Graf <graf@amazon.com>
Subject: Re: [PATCH v2] x86/PCI: Prefer MMIO over PIO on all hypervisor
Date: Mon, 03 Oct 2022 14:01:20 -0700 [thread overview]
Message-ID: <E522EECC-D20D-4A69-8A44-9CF2B36E2A29@zytor.com> (raw)
In-Reply-To: <87tu4l9cfm.fsf@redhat.com>
On October 3, 2022 8:03:41 AM PDT, Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>Ajay Kaher <akaher@vmware.com> writes:
>
>>> On 13/09/22, 7:05 PM, "Vitaly Kuznetsov" <vkuznets@redhat.com> wrote:
>>>>
>>>> Thanks Vitaly for your response.
>>>>
>>>> 1. we have multiple objects of struct pci_raw_ops, 2. adding 'priority' field to struct pci_raw_ops
>>>> doesn't seems to be appropriate as need to take decision which object of struct pci_raw_ops has
>>>> to be used, not something with-in struct pci_raw_ops.
>>>
>>> I'm not sure I follow, you have two instances of 'struct pci_raw_ops'
>>> which are called 'raw_pci_ops' and 'raw_pci_ext_ops'. What if you do
>>> something like (completely untested):
>>>
>>> diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
>>> index 70533fdcbf02..fb8270fa6c78 100644
>>> --- a/arch/x86/include/asm/pci_x86.h
>>> +++ b/arch/x86/include/asm/pci_x86.h
>>> @@ -116,6 +116,7 @@ extern void (*pcibios_disable_irq)(struct pci_dev *dev);
>>> extern bool mp_should_keep_irq(struct device *dev);
>>>
>>> struct pci_raw_ops {
>>> + int rating;
>>> int (*read)(unsigned int domain, unsigned int bus, unsigned int devfn,
>>> int reg, int len, u32 *val);
>>> int (*write)(unsigned int domain, unsigned int bus, unsigned int devfn,
>>> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
>>> index ddb798603201..e9965fd11576 100644
>>> --- a/arch/x86/pci/common.c
>>> +++ b/arch/x86/pci/common.c
>>> @@ -40,7 +40,8 @@ const struct pci_raw_ops *__read_mostly raw_pci_ext_ops;
>>> int raw_pci_read(unsigned int domain, unsigned int bus, unsigned int devfn,
>>> int reg, int len, u32 *val)
>>> {
>>> - if (domain == 0 && reg < 256 && raw_pci_ops)
>>> + if (domain == 0 && reg < 256 && raw_pci_ops &&
>>> + (!raw_pci_ext_ops || raw_pci_ext_ops->rating <= raw_pci_ops->rating))
>>> return raw_pci_ops->read(domain, bus, devfn, reg, len, val);
>>> if (raw_pci_ext_ops)
>>> return raw_pci_ext_ops->read(domain, bus, devfn, reg, len, val);
>>> @@ -50,7 +51,8 @@ int raw_pci_read(unsigned int domain, unsigned int bus, unsigned int devfn,
>>> int raw_pci_write(unsigned int domain, unsigned int bus, unsigned int devfn,
>>> int reg, int len, u32 val)
>>> {
>>> - if (domain == 0 && reg < 256 && raw_pci_ops)
>>> + if (domain == 0 && reg < 256 && raw_pci_ops &&
>>> + (!raw_pci_ext_ops || raw_pci_ext_ops->rating <= raw_pci_ops->rating))
>>> return raw_pci_ops->write(domain, bus, devfn, reg, len, val);
>>> if (raw_pci_ext_ops)
>>> return raw_pci_ext_ops->write(domain, bus, devfn, reg, len, val);
>>>
>>> and then somewhere in Vmware hypervisor initialization code
>>> (arch/x86/kernel/cpu/vmware.c) you do
>>>
>>> raw_pci_ext_ops->rating = 100;
>>
>> Thanks Vitaly, for your review and helping us to improve the code.
>>
>> I was working to make changes as you suggested, but before sending v3 would like to
>> discuss on following:
>>
>> If we add rating with-in struct pci_raw_ops then we can't have pci_mmcfg as const,
>> and following change is must in arch/x86/pci/mmconfig_64.c:
>>
>> -const struct pci_raw_ops pci_mmcfg = {
>> +struct pci_raw_ops pci_mmcfg = {
>> .read = pci_mmcfg_read,
>> .write = pci_mmcfg_write,
>> };
>>
>> So to avoid this change, is it fine to have global bool prefer_raw_pci_ext_ops?
>>
>> And raw_pci_read() will have following change:
>>
>> - if (domain == 0 && reg < 256 && raw_pci_ops)
>> + if (domain == 0 && reg < 256 && raw_pci_ops &&
>> + (!prefer_raw_pci_ext_ops || !raw_pci_ext_ops)
>>
>
>Not my but rather PCI maintainer's call but IMHO dropping 'const' is
>better, introducing a new global var is our 'last resort' and should be
>avoided whenever possible. Alternatively, you can add a
>raw_pci_ext_ops_preferred() function checking somethin within 'struct
>hypervisor_x86' but I'm unsure if it's better.
>
>Also, please check Alex' question/suggestion.
>
>...
>
Could this be ro_after_init?
prev parent reply other threads:[~2022-10-03 21:31 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-13 12:47 [PATCH v2] x86/PCI: Prefer MMIO over PIO on all hypervisor Ajay Kaher
2022-09-13 13:34 ` Vitaly Kuznetsov
2022-09-29 5:36 ` Ajay Kaher
2022-09-29 9:12 ` Alexander Graf
2022-10-03 15:03 ` Vitaly Kuznetsov
2022-10-03 17:34 ` Nadav Amit
2022-10-03 21:06 ` H. Peter Anvin
2022-10-03 21:28 ` Nadav Amit
2022-10-03 23:51 ` H. Peter Anvin
2022-10-04 0:19 ` Nadav Amit
2022-10-04 8:22 ` Alexander Graf
2022-10-04 18:48 ` Nadav Amit
2022-10-10 14:58 ` Nadav Amit
2022-10-10 17:05 ` Michael S. Tsirkin
2022-10-04 8:30 ` Vitaly Kuznetsov
2022-10-03 21:01 ` H. Peter Anvin [this message]
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