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Message-ID: <CAE9FiQXvYH4zCqp_uOb2nw7jvm8B=q3yx1tCjJUT+PkdymYEuw@mail.gmail.com>
Date: Fri, 25 May 2012 10:53:25 -0700
From: Yinghai Lu <yinghai@...nel.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Steven Newbury <steve@...wbury.org.uk>,
"H. Peter Anvin" <hpa@...or.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] PCI: Try to allocate mem64 above 4G at first
On Thu, May 24, 2012 at 9:36 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Wed, May 23, 2012 at 11:40:46AM -0700, Yinghai Lu wrote:
>> On Wed, May 23, 2012 at 10:30 AM, Yinghai Lu <yinghai@...nel.org> wrote:
>> > On Wed, May 23, 2012 at 8:57 AM, Linus Torvalds
>> > <torvalds@...ux-foundation.org> wrote:
>> >> On Tue, May 22, 2012 at 11:34 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>> >>> and will fall back to below 4g if it can not find any above 4g.
>> >>
>> >> Has this been tested on 32-bit machines without PAE? There might be
>> >> things that just happen to work because their allocations were always
>> >> done bottom-up.
>> >
>> > Good point. that problem should be addressed at first before this patch.
>>
>> Just checked code for 32bit machines without PAE.
>>
>> when X86_PAE is not set, phys_addr_t aka resource_size_t will be 32bit.
>> so in drivers/pci/bus.c::pci_bus_alloc_resource_fit()
>> will have bottom to 0.
>> resource_size_t bottom = PCIBIOS_MAX_MEM_32 + 1ULL;
>> also in arch/x86/kernel/setup.c::setup_arch()
>> iomem_resource.end = (1ULL << boot_cpu_data.x86_phys_bits) - 1;
>> will have iomem_resource.end to 0xffffffff
>>
>> when X86_PAE is set, but CPU does not support PAE.
>> phys_addr_t aka resource_size_t will be 32bit.
>
> I think you meant phys_addr_t and resource_size_t will be *64* bit
> when X86_PAE is set. Obvious to you, but quite confusing to non-x86
> experts like me :)
>
>> so in drivers/pci/bus.c::pci_bus_alloc_resource_fit()
>> will have bottom to 4g.
>> resource_size_t bottom = PCIBIOS_MAX_MEM_32 + 1ULL;
>> but
>> in arch/x86/kernel/setup.c::setup_arch()
>> iomem_resource.end = (1ULL << boot_cpu_data.x86_phys_bits) - 1;
>> will have iomem_resource.end to 0xffffffff, because x86_phys_bits is 32 when PAE
>> is not detected in arch/x86/kernel/cpu/common.c::get_cpu_cap.
>> that mean first try will fail, so it will go to second try with bottom to 0.
>>
>> so both case are safe with this patch.
>
> I don't really like the dependency on PCIBIOS_MAX_MEM_32 + 1ULL
> overflowing to zero -- that means the reader has to know what the
> value of PCIBIOS_MAX_MEM_32 is, and things would break in non-obvious
> ways if we changed it.
>
> What do you think of a patch like the following? It makes it
> explicit that we can only allocate space the CPU can address.
>
> commit feded2ae21d6160292726ccd5128080d42395be4
> Author: Bjorn Helgaas <bhelgaas@...gle.com>
> Date: Thu May 24 22:15:26 2012 -0600
>
> PCI: try to allocate 64-bit resources above 4GB
>
> If we have a 64-bit resource, try to allocate it above 4GB first. If that
> fails, either because there's no space or the CPU can't address space above
> 4GB (iomem_resource.end is the highest address the CPU supports), we'll
> fall back to allocating space below 4GB.
>
> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> index 4ce5ef2..2c56693 100644
> --- a/drivers/pci/bus.c
> +++ b/drivers/pci/bus.c
> @@ -121,14 +121,18 @@ pci_bus_alloc_resource(struct pci_bus *bus, struct resource *res,
> {
> int i, ret = -ENOMEM;
> struct resource *r;
> - resource_size_t max = -1;
> + resource_size_t start = 0;
> + resource_size_t end = PCIBIOS_MAX_MEM_32;
>
> type_mask |= IORESOURCE_IO | IORESOURCE_MEM;
>
> - /* don't allocate too high if the pref mem doesn't support 64bit*/
> - if (!(res->flags & IORESOURCE_MEM_64))
> - max = PCIBIOS_MAX_MEM_32;
> + /* If this is a 64-bit resource, prefer space above 4GB */
> + if (res->flags & IORESOURCE_MEM_64) {
> + start = PCIBIOS_MAX_MEM_32 + 1ULL;
> + end = iomem_resource.end;
but here we still have PCIBIOS_MAX_MEM_32 + 1ULL ...will still have
overflow to 0..
also because all mmio will in iomem_resource, so we don't need to
specify it, and still keep using -1 as max.
aka avoid referring global iomem_resource here.
So this version is the same as old version, and just reverse checking
res->flags & IORESOURCE_MEM_64
> + }
>
> +again:
> pci_bus_for_each_resource(bus, r, i) {
> if (!r)
> continue;
> @@ -145,12 +149,18 @@ pci_bus_alloc_resource(struct pci_bus *bus, struct resource *res,
>
> /* Ok, try it out.. */
> ret = allocate_resource(r, res, size,
> - r->start ? : min,
> - max, align,
> + max(start, r->start ? : min),
> + end, align,
> alignf, alignf_data);
> if (ret == 0)
> - break;
> + return 0;
> }
> +
> + if (start != 0) {
> + start = 0;
> + goto again;
> + }
> +
> return ret;
> }
>
--
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