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Date: Thu, 25 Jan 2024 17:43:56 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Audra Mitchell <audra@redhat.com>
Cc: shuah@kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org, raquini@redhat.com, Adam Sindelar
 <adam@wowsignal.io>
Subject: Re: [PATCH] selftests/mm: Update va_high_addr_switch.sh to check
 CPU for la57 flag
Message-Id: <20240125174356.199f44f329e137f9a6437648@linux-foundation.org>
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On Wed, 24 Jan 2024 08:39:33 -0500 Audra Mitchell <audra@redhat.com> wrote:

> > A more complete description of these "test failures" would be helpful
> > please.
> > 
> 
> Hey, sorry for the incomplete description. The test does a series of mmap
> calls including three using the MAP_FIXED flag and specifying an address that
> is 1<<47 or 1<<48. These addresses are only available if you are using level 5
> page tables, which requires both the CPU to have the capabiltiy (la57 flag)
> and the kernel to be configured. Currently the test only checks for the kernel
> configuration option, so this test can still report a false positive. Here are
> the three failing lines:
> 
> $ ./va_high_addr_switch | grep FAILED
> mmap(ADDR_SWITCH_HINT, 2 * PAGE_SIZE, MAP_FIXED): 0xffffffffffffffff - FAILED
> mmap(HIGH_ADDR, MAP_FIXED): 0xffffffffffffffff - FAILED
> mmap(ADDR_SWITCH_HINT, 2 * PAGE_SIZE, MAP_FIXED): 0xffffffffffffffff - FAILED
> 
> I thought (for about a second) refactoring the test so that these three mmap
> calls will only be run on systems with the level 5 page tables available, but
> the whole point of the test is to check the level 5 feature...
> 
> If you would like me to also update the description on the patch let me know
> and I'll update it and resubmit. Thanks!

I pasted the above into the changelog, thanks.