From: Yan Zhao <yan.y.zhao@intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Linus Walleij <linus.walleij@linaro.org>,
guoren <guoren@kernel.org>, Brian Cain <bcain@quicinc.com>,
Jonas Bonn <jonas@southpole.se>,
"Stefan Kristiansson" <stefan.kristiansson@saunalahti.fi>,
Stafford Horne <shorne@gmail.com>,
Linux-Arch <linux-arch@vger.kernel.org>,
<linux-kernel@vger.kernel.org>,
"linux-csky@vger.kernel.org" <linux-csky@vger.kernel.org>,
<linux-hexagon@vger.kernel.org>,
"linux-openrisc@vger.kernel.org" <linux-openrisc@vger.kernel.org>
Subject: Re: [PATCH 0/4] apply page shift to PFN instead of VA in pfn_to_virt
Date: Thu, 1 Feb 2024 08:01:53 +0800 [thread overview]
Message-ID: <ZbrfcTaiuu2gaa2A@yzhao56-desk.sh.intel.com> (raw)
In-Reply-To: <5e55b5c0-6c8d-45b4-ac04-cf694bcb08d3@app.fastmail.com>
On Wed, Jan 31, 2024 at 12:48:38PM +0100, Arnd Bergmann wrote:
> On Wed, Jan 31, 2024, at 06:51, Yan Zhao wrote:
> > This is a tiny fix to pfn_to_virt() for some platforms.
> >
> > The original implementaion of pfn_to_virt() takes PFN instead of PA as the
> > input to macro __va, with PAGE_SHIFT applying to the converted VA, which
> > is not right under most conditions, especially when there's an offset in
> > __va.
> >
> >
> > Yan Zhao (4):
> > asm-generic/page.h: apply page shift to PFN instead of VA in
> > pfn_to_virt
> > csky: apply page shift to PFN instead of VA in pfn_to_virt
> > Hexagon: apply page shift to PFN instead of VA in pfn_to_virt
> > openrisc: apply page shift to PFN instead of VA in pfn_to_virt
>
> Nice catch, this is clearly a correct fix, and I can take
> the series through the asm-generic tree if we want to take
> this approach.
>
> I made a couple of interesting observations looking at this patch
> though:
>
> - this function is only used in architecture specific code on
> m68k, riscv and s390, though a couple of other architectures
> have the same definition.
>
> - There is another function that does the same thing called
> pfn_to_kaddr(), which is defined on arm, arm64, csky,
> loongarch, mips, nios2, powerpc, s390, sh, sparc and x86,
> as well as yet another pfn_va() on parisc.
>
> - the asm-generic/page.h file used to be included by h8300, c6x
> and blackfin, all of which are now gone. It has no users left
> and can just as well get removed, unless we find a new use
> for it.
>
> Since it looks like the four broken functions you fix
> don't have a single caller, maybe it would be better to
> just remove them all?
>
> How exactly did you notice the function being wrong,
> did you try to add a user somewhere, or just read through
> the code?
I came across them when I was debugging an unexpected kernel page fault
on x86, and I was not sure whether page_to_virt() was compiled in
asm-generic/page.h or linux/mm.h.
Though finally, it turned out that the one in linux/mm.h was used, which
yielded the right result and the unexpected kernel page fault in my case
was not related to page_to_virt(), it did lead me to noticing that the
pfn_to_virt() in asm-generic/page.h and other 3 archs did not look right.
Yes, unlike virt_to_pfn() which still has a caller in openrisc (among
csky, Hexagon, openrisc), pfn_to_virt() now does not have a caller in
the 3 archs. Though both virt_to_pfn() and pfn_to_virt() are referenced
in asm-generic/page.h, I also not sure if we need to remove the
asm-generic/page.h which may serve as a template to future archs ?
So, either way looks good to me :)
next prev parent reply other threads:[~2024-02-01 0:31 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-31 5:51 [PATCH 0/4] apply page shift to PFN instead of VA in pfn_to_virt Yan Zhao
2024-01-31 5:57 ` [PATCH 1/4] asm-generic/page.h: " Yan Zhao
2024-02-23 11:26 ` Guo Ren
2024-02-29 13:34 ` Linus Walleij
2024-02-29 23:01 ` Yan Zhao
2024-01-31 5:59 ` [PATCH 2/4] csky: " Yan Zhao
2024-02-23 11:26 ` Guo Ren
2024-01-31 6:00 ` [PATCH 3/4] Hexagon: " Yan Zhao
2024-01-31 6:01 ` [PATCH 4/4] openrisc: " Yan Zhao
2024-01-31 7:37 ` [PATCH 0/4] " Linus Walleij
2024-01-31 11:48 ` Arnd Bergmann
2024-02-01 0:01 ` Yan Zhao [this message]
2024-02-01 5:46 ` Arnd Bergmann
2024-02-01 10:46 ` Geert Uytterhoeven
2024-02-02 7:27 ` Arnd Bergmann
2024-02-02 1:02 ` Yan Zhao
2024-02-02 7:04 ` Arnd Bergmann
2024-02-02 14:09 ` Yan Zhao
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