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Date: Fri, 8 Mar 2024 09:02:11 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-mm <linux-mm@kvack.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Daniel Borkmann <daniel@iogearbox.net>, bpf <bpf@vger.kernel.org>,
	Bjorn Helgaas <bhelgaas@google.com>, linux-pci@vger.kernel.org
Subject: Re: vm_area at addr ffffffffc0800000 is not marked as VM_IOREMAP
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On Fri, Mar 08, 2024 at 08:33:18AM -0800, Alexei Starovoitov wrote:
> vmap_range_noflush() is static in mm/vmalloc.c
> There is vmap_pages_range_noflush() that is in mm/internal.h,
> but it needs pages instead of phys_addr_t.
> Newly introduced vm_area_map_pages() needs struct vm_struct *area
> and struct page **pages.
> In this PCI case there is no vm_struct and no pages.
> ioremap_page_range() is the only api that fits. afaict.

Except that we want to enforce a vm_area with the ioremap flag for
ioremap_page_range, and just adding a NULL check defeats that.

The right long term thing would be to actually create a vm_area
for the PCI_IOBASE region, but until then we just need a lower level
API.  That's why I suggest to add a vmap_range() that is basically
the ioremap_page_range before you added the checks, and make
ioremap_page_range a wrapper around that that checks the area.

If/when we get PCI_IOBASE handling converted to the proper
vmalloc/ioremap areas we can remove that again as well as
vunmap_range which is just used for PCI_IOBASE and other equivalent
ISA_IO_BASE in powerpc and somewhat unusual case in arm64 that I
need to look into a bit more.