Re: [PATCH v3] x86/PCI: Ignore E820 reservations for bridge windows on newer systems

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 10/14/21 2:06 PM, Rafael J. Wysocki wrote:
> On Thu, Oct 14, 2021 at 1:24 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>
>> Hi,
>>
>> On 14-10-2021 13:14, Rafael J. Wysocki wrote:
>>> On Thu, Oct 14, 2021 at 1:04 PM Hans de Goede <hdegoede@redhat.com> wrote:
>>>>
>>>> Some BIOS-es contain a bug where they add addresses which map to system RAM
>>>> in the PCI bridge memory window returned by the ACPI _CRS method, see
>>>> commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address
>>>> space").
>>>>
>>>> To avoid this Linux by default excludes E820 reservations when allocating
>>>> addresses since 2010. Windows however ignores E820 reserved regions for PCI
>>>> mem allocations, so in hindsight Linux honoring them is a problem.
>>>>
>>>> Recently (2020) some systems have shown-up with E820 reservations which
>>>> cover the entire _CRS returned PCI bridge memory window, causing all
>>>> attempts to assign memory to PCI BARs which have not been setup by the
>>>> BIOS to fail. For example here are the relevant dmesg bits from a
>>>> Lenovo IdeaPad 3 15IIL 81WE:
>>>>
>>>>  [mem 0x000000004bc50000-0x00000000cfffffff] reserved
>>>>  pci_bus 0000:00: root bus resource [mem 0x65400000-0xbfffffff window]
>>>>
>>>> Ideally Linux would fully stop honoring E820 reservations for PCI mem
>>>> allocations, but then the old systems this was added for will regress.
>>>> Instead keep the old behavior for old systems, while ignoring the E820
>>>> reservations like Windows does for any systems from now on.
>>>>
>>>> Old systems are defined here as BIOS year < 2018, this was chosen to
>>>> make sure that pci_use_e820 will not be set on the currently affected
>>>> systems, while at the same time also taking into account that the
>>>> systems for which the E820 checking was originally added may have
>>>> received BIOS updates for quite a while (esp. CVE related ones),
>>>> giving them a more recent BIOS year then 2010.
>>>>
>>>> Also add pci=no_e820 and pci=use_e820 options to allow overriding
>>>> the BIOS year heuristic.
>>>>
>>>> BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=206459
>>>> BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1868899
>>>> BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=1871793
>>>> BugLink: https://bugs.launchpad.net/bugs/1878279
>>>> BugLink: https://bugs.launchpad.net/bugs/1931715
>>>> BugLink: https://bugs.launchpad.net/bugs/1932069
>>>> BugLink: https://bugs.launchpad.net/bugs/1921649
>>>> Cc: Benoit Grégoire <benoitg@coeus.ca>
>>>> Cc: Hui Wang <hui.wang@canonical.com>
>>>> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
>>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>>
>>> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>
>> Thank you.
>>
>>> with one tiny nit below.
>>>
>>> Or please let me know if you want me to pick this up.
>>
>> Since all of the changes are under arch/x86/ I expect the x86/tip
>> folks to pick this up ?
> 
> OK
> 
>>>
>>>> ---
>>>> Changes in v3:
>>>> - Commit msg tweaks (drop dmesg timestamps, typo fix)
>>>> - Use "defined(CONFIG_...)" instead of "defined CONFIG_..."
>>>> - Add Mika's Reviewed-by
>>>>
>>>> Changes in v2:
>>>> - Replace the per model DMI quirk approach with disabling E820 reservations
>>>>   checking for all systems with a BIOS year >= 2018
>>>> - Add documentation for the new kernel-parameters to
>>>>   Documentation/admin-guide/kernel-parameters.txt
>>>> ---
>>>> Other patches trying to address the same issue:
>>>> https://lore.kernel.org/r/20210624095324.34906-1-hui.wang@canonical.com
>>>> https://lore.kernel.org/r/20200617164734.84845-1-mika.westerberg@linux.intel.com
>>>> V1 patch:
>>>> https://lore.kernel.org/r/20211005150956.303707-1-hdegoede@redhat.com
>>>> ---
>>>>  .../admin-guide/kernel-parameters.txt         |  6 ++++
>>>>  arch/x86/include/asm/pci_x86.h                | 10 +++++++
>>>>  arch/x86/kernel/resource.c                    |  4 +++
>>>>  arch/x86/pci/acpi.c                           | 29 +++++++++++++++++++
>>>>  arch/x86/pci/common.c                         |  6 ++++
>>>>  5 files changed, 55 insertions(+)
>>>>
>>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>>> index 43dc35fe5bc0..969cde5d74c8 100644
>>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>>> @@ -3949,6 +3949,12 @@
>>>>                                 please report a bug.
>>>>                 nocrs           [X86] Ignore PCI host bridge windows from ACPI.
>>>>                                 If you need to use this, please report a bug.
>>>> +               use_e820        [X86] Honor E820 reservations when allocating
>>>> +                               PCI host bridge memory. If you need to use this,
>>>> +                               please report a bug.
>>>> +               no_e820         [X86] ignore E820 reservations when allocating
>>>> +                               PCI host bridge memory. If you need to use this,
>>>> +                               please report a bug.
>>>>                 routeirq        Do IRQ routing for all PCI devices.
>>>>                                 This is normally done in pci_enable_device(),
>>>>                                 so this option is a temporary workaround
>>>> diff --git a/arch/x86/include/asm/pci_x86.h b/arch/x86/include/asm/pci_x86.h
>>>> index 490411dba438..0bb4e7dd0ffc 100644
>>>> --- a/arch/x86/include/asm/pci_x86.h
>>>> +++ b/arch/x86/include/asm/pci_x86.h
>>>> @@ -39,6 +39,8 @@ do {                                          \
>>>>  #define PCI_ROOT_NO_CRS                0x100000
>>>>  #define PCI_NOASSIGN_BARS      0x200000
>>>>  #define PCI_BIG_ROOT_WINDOW    0x400000
>>>> +#define PCI_USE_E820           0x800000
>>>> +#define PCI_NO_E820            0x1000000
>>>>
>>>>  extern unsigned int pci_probe;
>>>>  extern unsigned long pirq_table_addr;
>>>> @@ -64,6 +66,8 @@ void pcibios_scan_specific_bus(int busn);
>>>>
>>>>  /* pci-irq.c */
>>>>
>>>> +struct pci_dev;
>>>> +
>>>>  struct irq_info {
>>>>         u8 bus, devfn;                  /* Bus, device and function */
>>>>         struct {
>>>> @@ -232,3 +236,9 @@ static inline void mmio_config_writel(void __iomem *pos, u32 val)
>>>>  # define x86_default_pci_init_irq      NULL
>>>>  # define x86_default_pci_fixup_irqs    NULL
>>>>  #endif
>>>> +
>>>> +#if defined(CONFIG_PCI) && defined(CONFIG_ACPI)
>>>> +extern bool pci_use_e820;
>>>> +#else
>>>> +#define pci_use_e820 false
>>>> +#endif
>>>> diff --git a/arch/x86/kernel/resource.c b/arch/x86/kernel/resource.c
>>>> index 9b9fb7882c20..e8dc9bc327bd 100644
>>>> --- a/arch/x86/kernel/resource.c
>>>> +++ b/arch/x86/kernel/resource.c
>>>> @@ -1,6 +1,7 @@
>>>>  // SPDX-License-Identifier: GPL-2.0
>>>>  #include <linux/ioport.h>
>>>>  #include <asm/e820/api.h>
>>>> +#include <asm/pci_x86.h>
>>>>
>>>>  static void resource_clip(struct resource *res, resource_size_t start,
>>>>                           resource_size_t end)
>>>> @@ -28,6 +29,9 @@ static void remove_e820_regions(struct resource *avail)
>>>>         int i;
>>>>         struct e820_entry *entry;
>>>>
>>>> +       if (!pci_use_e820)
>>>> +               return;
>>>> +
>>>>         for (i = 0; i < e820_table->nr_entries; i++) {
>>>>                 entry = &e820_table->entries[i];
>>>>
>>>> diff --git a/arch/x86/pci/acpi.c b/arch/x86/pci/acpi.c
>>>> index 948656069cdd..6c2febe84b6f 100644
>>>> --- a/arch/x86/pci/acpi.c
>>>> +++ b/arch/x86/pci/acpi.c
>>>> @@ -21,6 +21,8 @@ struct pci_root_info {
>>>>
>>>>  static bool pci_use_crs = true;
>>>>  static bool pci_ignore_seg = false;
>>>> +/* Consumed in arch/x86/kernel/resource.c */
>>>> +bool pci_use_e820 = false;
>>>>
>>>>  static int __init set_use_crs(const struct dmi_system_id *id)
>>>>  {
>>>> @@ -160,6 +162,33 @@ void __init pci_acpi_crs_quirks(void)
>>>>                "if necessary, use \"pci=%s\" and report a bug\n",
>>>>                pci_use_crs ? "Using" : "Ignoring",
>>>>                pci_use_crs ? "nocrs" : "use_crs");
>>>> +
>>>> +       /*
>>>> +        * Some BIOS-es contain a bug where they add addresses which map to system
>>>> +        * RAM in the PCI bridge memory window returned by the ACPI _CRS method, see
>>>> +        * commit 4dc2287c1805 ("x86: avoid E820 regions when allocating address space").
>>>> +        * To avoid this Linux by default excludes E820 reservations when allocating
>>>> +        * addresses since 2010. Windows however ignores E820 reserved regions for
>>>> +        * PCI mem allocations, so in hindsight Linux honoring them is a problem.
>>>> +        * In 2020 some systems have shown-up with E820 reservations which cover the
>>>> +        * entire _CRS returned PCI bridge memory window, causing all attempts to
>>>> +        * assign memory to PCI BARs to fail if Linux honors the E820 reservations.
>>>> +        *
>>>> +        * Ideally Linux would fully stop honoring E820 reservations for PCI mem
>>>> +        * allocations, but then the old systems this was added for will regress.
>>>> +        * Instead keep the old behavior for old systems, while ignoring the E820
>>>> +        * reservations like Windows does for any systems from now on.
>>>> +        */
>>>> +       if (year >= 0 && year < 2018)
>>>> +               pci_use_e820 = true;
>>>> +
>>>> +       if (pci_probe & PCI_NO_E820)
>>>> +               pci_use_e820 = false;
>>>> +       else if (pci_probe & PCI_USE_E820)
>>>> +               pci_use_e820 = true;
>>>> +
>>>> +       printk(KERN_INFO "PCI: %s E820 reservations for host bridge windows\n",
>>>> +              pci_use_e820 ? "Honoring" : "Ignoring");
>>>
>>> Why not pr_info()?
>>
>> This file is using printk(KERN_... consistently everywhere. I'm just following
>> the existing style here. I very much dislike mixing styles in a single file.
> 
> In this particular case, it isn't just a matter of style.

Without a #define pr_fmt in the file there is no functional difference.

> Also, if what is regarded as a good practice has changed since the
> file was created, should new code added to it be prevented from
> following the new good practice, because the old code didn't follow
> it?

That is a non trivial question to answer, e.g. using devm_ functions
while the rest of the driver is not using them can be tricky and it
might be better to convert the whole driver over to devm_ use in one go.

>> If we want to change this for this file then IMHO the right thing to do would
>> be a follow up patch changing all the printk-s at once.
> 
> I would do the pr_info() here in this patch and change the rest of the
> file to follow in a subsequent patch.

All printk's in this file are prefixed with "PCI: " so converting to
pr_info() should probably involve adding this:

#define pr_fmt(fmt) "PCI: " fmt

So should I add that already while using pr_info() in this patch,
which would look weird / look like an unrelated change?

Or should I not add that and manually add the "PCI: " prefix,
requiring the pr_info to still be replaced in a subsequent patch
converting the rest over to pr_info() ?

IMHO it makes the most sense to keep printk here and then
replace the printk with a pr_info, dropping the "PCI: "
prefix in a subsequent patch converting all the printk-s.

That would also make the subsequent patch cleaner, because
replacing a pr_info with a pr_info in that patch would
look weird.

Regards,

Hans