Re: [PATCH v5 1/5] x86/quirks: Fix stolen detection with integrated + discrete GPU

[Borislav Petkov <bp@alien8.de>]

n Thu, Jan 13, 2022 at 04:28:39PM -0800, Lucas De Marchi wrote:
> early_pci_scan_bus() does a depth-first traversal, possibly calling
> the quirk functions for each device based on vendor, device and class
> from early_qrk table. intel_graphics_quirks() however uses PCI_ANY_ID
> and does additional filtering in the quirk.
> 
> If there is an Intel integrated + discrete GPU the quirk may be called
> first for the discrete GPU based on the PCI topology. Then we will fail
> to reserve the system stolen memory for the integrated GPU, because we
> will already have marked the quirk as "applied".

Who is "we"?

Please use passive voice in your commit message: no "we" or "I", etc,
and describe your changes in imperative mood.

Bottom line is: personal pronouns are ambiguous in text, especially with
so many parties/companies/etc developing the kernel so let's avoid them
please.

> This was reproduced in a setup with Alderlake-P (integrated) + DG2
> (discrete), with the following PCI topology:
> 
> 	- 00:01.0 Bridge
> 	  `- 03:00.0 DG2
> 	- 00:02.0 Integrated GPU
> 
> So, stop using the QFLAG_APPLY_ONCE flag, replacing it with a static
> local variable. We can set this variable in the right place, inside
> intel_graphics_quirks(), only when the quirk was actually applied, i.e.
> when we find the integrated GPU based on the intel_early_ids table.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
> ---
> 
> v5: apply fix before the refactor
> 
>  arch/x86/kernel/early-quirks.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
> index 1ca3a56fdc2d..de9a76eb544e 100644
> --- a/arch/x86/kernel/early-quirks.c
> +++ b/arch/x86/kernel/early-quirks.c
> @@ -589,10 +589,14 @@ intel_graphics_stolen(int num, int slot, int func,
>  
>  static void __init intel_graphics_quirks(int num, int slot, int func)
>  {
> +	static bool quirk_applied __initdata;
>  	const struct intel_early_ops *early_ops;
>  	u16 device;
>  	int i;
>  
> +	if (quirk_applied)
> +		return;
> +
>  	device = read_pci_config_16(num, slot, func, PCI_DEVICE_ID);
>  
>  	for (i = 0; i < ARRAY_SIZE(intel_early_ids); i++) {
> @@ -605,6 +609,8 @@ static void __init intel_graphics_quirks(int num, int slot, int func)
>  
>  		intel_graphics_stolen(num, slot, func, early_ops);
>  
> +		quirk_applied = true;
> +
>  		return;
>  	}

So I wonder: why can't you simply pass in a static struct chipset *
pointer into the early_qrk[i].f function and in there you can set
QFLAG_APPLIED or so, so that you can mark that the quirk is applied by
using the nice, per-quirk flags someone has already added instead of
this ugly static variable?

Patch 3 especially makes me go, huh?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette