linux-kernel - Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,

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Date:   Sun, 29 Aug 2021 22:11:46 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Richard Henderson <rth@...ddle.net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        James E J Bottomley <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        "David S . Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        X86 ML <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        linux-alpha@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v4 11/15] pci: Add pci_iomap_shared{,_range}


On 8/29/2021 3:26 PM, Michael S. Tsirkin wrote:
> On Sun, Aug 29, 2021 at 09:17:53AM -0700, Andi Kleen wrote:
>> Also I changing this single call really that bad? It's not that we changing
>> anything drastic here, just give the low level subsystem a better hint about
>> the intention. If you don't like the function name, could make it an
>> argument instead?
> My point however is that the API should say that the
> driver has been audited,

We have that status in the struct device. If you want to tie the ioremap 
to that we could define a ioremap_device() with a device argument and 
decide based on that.

Or we can add _audited to the name. ioremap_shared_audited?

> not that the mapping has been
> done in some special way. For example the mapping can be
> in some kind of wrapper, not directly in the driver.
> However you want the driver validated, not the wrapper.
>
> Here's an idea:


I don't think magic differences of API behavior based on some define are 
a good idea.  That's easy to miss.

That's a "COME FROM" in API design.

Also it wouldn't handle the case that a driver has both private and 
shared ioremaps, e.g. for BIOS structures.

And we've been avoiding that drivers can self declare auditing, we've 
been trying to have a separate centralized list so that it's easier to 
enforce and avoids any cut'n'paste mistakes.

-Andi