[PATCH] arm64: Fix kernel address detection of __is_lm_address()

[Catalin Marinas]

On Tue, Jan 26, 2021 at 01:40:56PM +0000, Vincenzo Frascino wrote:
> Currently, the __is_lm_address() check just masks out the top 12 bits
> of the address, but if they are 0, it still yields a true result.
> This has as a side effect that virt_addr_valid() returns true even for
> invalid virtual addresses (e.g. 0x0).
> 
> Fix the detection checking that it's actually a kernel address starting
> at PAGE_OFFSET.
> 
> Fixes: f4693c2716b35 ("arm64: mm: extend linear region for 52-bit VA configurations")
> Cc: <stable at vger.kernel.org> # 5.4.x

Not sure what happened with the Fixes tag but that's definitely not what
it fixes. The above is a 5.11 commit that preserves the semantics of an
older commit. So it should be:

Fixes: 68dd8ef32162 ("arm64: memory: Fix virt_addr_valid() using __is_lm_address()")

The above also had a fix for another commit but no need to add two
entries, we just fix the original fix: 14c127c957c1 ("arm64: mm: Flip
kernel VA space").

Anyway, no need to repost, I can update the fixes tag myself.

In terms of stable backports, it may be cleaner to backport 7bc1a0f9e176
("arm64: mm: use single quantity to represent the PA to VA translation")
which has a Fixes tag already but never made it to -stable. On top of
this, we can backport Ard's latest f4693c2716b35 ("arm64: mm: extend
linear region for 52-bit VA configurations"). I just tried these locally
and the conflicts were fairly trivial.

-- 
Catalin