linux-kernel - Re: [PATCH v3 1/7] swiotlb: make io_tlb_default

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Message-ID: <20230627192414.6b78fdb8@meshulam.tesarici.cz>
Date:   Tue, 27 Jun 2023 19:24:14 +0200
From:   Petr Tesařík <petr@...arici.cz>
To:     Christoph Hellwig <hch@....de>
Cc:     Robin Murphy <robin.murphy@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Petr Tesarik <petrtesarik@...weicloud.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Kees Cook <keescook@...omium.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "moderated list:XEN HYPERVISOR ARM" <xen-devel@...ts.xenproject.org>,
        "moderated list:ARM PORT" <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:MIPS" <linux-mips@...r.kernel.org>,
        "open list:XEN SWIOTLB SUBSYSTEM" <iommu@...ts.linux.dev>,
        Roberto Sassu <roberto.sassu@...weicloud.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>
Subject: Re: [PATCH v3 1/7] swiotlb: make io_tlb_default_mem local to
 swiotlb.c

On Tue, 27 Jun 2023 17:48:02 +0200
Christoph Hellwig <hch@....de> wrote:

> On Tue, Jun 27, 2023 at 01:30:06PM +0200, Petr Tesařík wrote:
> > Xen is the only user of an "is SWIOTLB present" interface. IIUC Xen
> > needs bounce buffers for the PCI frontend driver, but if there is no
> > other reason to have a SWIOTLB, the system does not set up one at boot.  
> 
> Please take a look at my "unexport swiotlb_active v2" series that
> unfortunately missed the 6.5 merge window waiting for reviews.

I noticed it, but it seems I missed the part which completely removes
pci_xen_swiotlb_init_late().

Then we're left only with a reference from xen_mm_init() in
arch/arm/xen/mm.c, and I believe this one can also be solved
differently.

Petr T