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From: Mike Rapoport <rppt@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guillaume Tucker <gtucker@collabora.com>,
	Mark Brown <broonie@kernel.org>,
	Mark-PK Tsai <mark-pk.tsai@mediatek.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Russell King <linux@armlinux.org.uk>,
	Tony Lindgren <tony@atomide.com>, Will Deacon <will@kernel.org>,
	"kernelci . org bot" <bot@kernelci.org>,
	kernelci-results@groups.io,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"# 3.4.x" <stable@vger.kernel.org>
Subject: Re: [PATCH] arm[64]/memremap: don't abuse pfn_valid() to ensure presence of linear map
Date: Mon, 25 Apr 2022 06:58:08 +0300	[thread overview]
Message-ID: <YmYcUEZfyk1FbJyW@kernel.org> (raw)
In-Reply-To: <CAMj1kXGzL2u1gOBs7EutZXXej-2-a+EouEZySXXsQ0Dz0gaKTA@mail.gmail.com>

On Sun, Apr 24, 2022 at 11:19:05PM +0200, Ard Biesheuvel wrote:
> On Sun, 24 Apr 2022 at 19:22, Mike Rapoport <rppt@kernel.org> wrote:
> >
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > The semantics of pfn_valid() is to check presence of the memory map for a
> > PFN and not whether a PFN is covered by the linear map. The memory map may
> > be present for NOMAP memory regions, but they won't be mapped in the linear
> > mapping.  Accessing such regions via __va() when they are memremap()'ed
> > will cause a crash.

...

> > diff --git a/kernel/iomem.c b/kernel/iomem.c
> > index 62c92e43aa0d..e85bed24c0a9 100644
> > --- a/kernel/iomem.c
> > +++ b/kernel/iomem.c
> > @@ -33,7 +33,7 @@ static void *try_ram_remap(resource_size_t offset, size_t size,
> >         unsigned long pfn = PHYS_PFN(offset);
> >
> >         /* In the simple case just return the existing linear address */
> > -       if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)) &&
> > +       if (!PageHighMem(pfn_to_page(pfn)) &&
> 
> This looks wrong to me. Calling any of the PageXxx() accessors is only
> safe if the PFN is valid, since otherwise, we don't know if the
> associated struct page exists.

Yeah, you are right, was over-enthusiastic here...
 
> >             arch_memremap_can_ram_remap(offset, size, flags))
> >                 return __va(offset);
> >
> >
> > base-commit: b2d229d4ddb17db541098b83524d901257e93845
> > --
> > 2.28.0
> >

-- 
Sincerely yours,
Mike.

WARNING: multiple messages have this Message-ID (diff)
From: Mike Rapoport <rppt@kernel.org>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Guillaume Tucker <gtucker@collabora.com>,
	Mark Brown <broonie@kernel.org>,
	Mark-PK Tsai <mark-pk.tsai@mediatek.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Russell King <linux@armlinux.org.uk>,
	Tony Lindgren <tony@atomide.com>, Will Deacon <will@kernel.org>,
	"kernelci . org bot" <bot@kernelci.org>,
	kernelci-results@groups.io,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"# 3.4.x" <stable@vger.kernel.org>
Subject: Re: [PATCH] arm[64]/memremap: don't abuse pfn_valid() to ensure presence of linear map
Date: Mon, 25 Apr 2022 06:58:08 +0300	[thread overview]
Message-ID: <YmYcUEZfyk1FbJyW@kernel.org> (raw)
In-Reply-To: <CAMj1kXGzL2u1gOBs7EutZXXej-2-a+EouEZySXXsQ0Dz0gaKTA@mail.gmail.com>

On Sun, Apr 24, 2022 at 11:19:05PM +0200, Ard Biesheuvel wrote:
> On Sun, 24 Apr 2022 at 19:22, Mike Rapoport <rppt@kernel.org> wrote:
> >
> > From: Mike Rapoport <rppt@linux.ibm.com>
> >
> > The semantics of pfn_valid() is to check presence of the memory map for a
> > PFN and not whether a PFN is covered by the linear map. The memory map may
> > be present for NOMAP memory regions, but they won't be mapped in the linear
> > mapping.  Accessing such regions via __va() when they are memremap()'ed
> > will cause a crash.

...

> > diff --git a/kernel/iomem.c b/kernel/iomem.c
> > index 62c92e43aa0d..e85bed24c0a9 100644
> > --- a/kernel/iomem.c
> > +++ b/kernel/iomem.c
> > @@ -33,7 +33,7 @@ static void *try_ram_remap(resource_size_t offset, size_t size,
> >         unsigned long pfn = PHYS_PFN(offset);
> >
> >         /* In the simple case just return the existing linear address */
> > -       if (pfn_valid(pfn) && !PageHighMem(pfn_to_page(pfn)) &&
> > +       if (!PageHighMem(pfn_to_page(pfn)) &&
> 
> This looks wrong to me. Calling any of the PageXxx() accessors is only
> safe if the PFN is valid, since otherwise, we don't know if the
> associated struct page exists.

Yeah, you are right, was over-enthusiastic here...
 
> >             arch_memremap_can_ram_remap(offset, size, flags))
> >                 return __va(offset);
> >
> >
> > base-commit: b2d229d4ddb17db541098b83524d901257e93845
> > --
> > 2.28.0
> >

-- 
Sincerely yours,
Mike.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2022-04-25  3:58 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-24 17:20 [PATCH] arm[64]/memremap: don't abuse pfn_valid() to ensure presence of linear map Mike Rapoport
2022-04-24 17:20 ` Mike Rapoport
2022-04-24 20:14 ` kernel test robot
2022-04-24 20:14   ` kernel test robot
2022-04-24 20:14 ` kernel test robot
2022-04-24 20:14   ` kernel test robot
2022-04-24 21:19 ` Ard Biesheuvel
2022-04-24 21:19   ` Ard Biesheuvel
2022-04-25  3:58   ` Mike Rapoport [this message]
2022-04-25  3:58     ` Mike Rapoport

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