linux-kernel - Re: [RFC PATCH] PCI: Add quirk to always map ivshmem as write-back

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Message-ID: <20250917183821.GDaMsAHa7kVPBt5HAV@fat_crate.local>
Date: Wed, 17 Sep 2025 20:38:21 +0200
From: Borislav Petkov <bp@...en8.de>
To: Alexey Kardashevskiy <aik@....com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Kai-Heng Feng <kai.heng.feng@...onical.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Santosh Shukla <santosh.shukla@....com>,
	"Nikunj A. Dadhania" <nikunj@....com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH] PCI: Add quirk to always map ivshmem as write-back

On Mon, Sep 15, 2025 at 05:43:33PM +1000, Alexey Kardashevskiy wrote:
> yeah, sadly, there is one - people are actually using it, for, like,
> a decade, and not exactly keen on changing those user space tools :) Hence
> "RFC".

Then this commit message needs a lot more explanation as it is something the
kernel should support apparently when running as a guest...

But then, if it has been used for a decade already, why do you need that quirk
now? No one has noticed in 10 years time...?

> > >   	else
> > > +	else if (!(pci_resource_flags(pdev, bar) & IORESOURCE_CACHEABLE))
> > 	^^^^^^
> > 
> > This can't build.
> 
> Why? Compiles and works just fine.

Here's a more detailed explanation:

https://lore.kernel.org/r/202506131608.QlkxUPnI-lkp@intel.com

You haven't replaced the "else" with "else if" but left it there.

Thx.

-- 
Regards/Gruss,
    Boris.

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