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From:   Martin Fernandez <martin.fernandez@eclypsium.com>
Date:   Tue, 8 Feb 2022 18:09:31 -0300
Message-ID: <CAKgze5YtTMmmqmrNjkCey84nSRxGpa_yajH8+9kwQLckb2dFoA@mail.gmail.com>
Subject: Re: [PATCH v6 3/6] x86/e820: Refactor range_update and range_remove
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org, linux-efi@vger.kernel.org,
        platform-driver-x86@vger.kernel.org, linux-mm@kvack.org,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
        dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
        ardb@kernel.org, dvhart@infradead.org, andy@infradead.org,
        gregkh@linuxfoundation.org, rafael@kernel.org, rppt@kernel.org,
        akpm@linux-foundation.org, daniel.gutson@eclypsium.com,
        hughsient@gmail.com, alex.bazhaniuk@eclypsium.com,
        alison.schofield@intel.com
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On 2/7/22, Kees Cook <keescook@chromium.org> wrote:
> On Thu, Feb 03, 2022 at 01:43:25PM -0300, Martin Fernandez wrote:
>> __e820__range_update and e820__range_remove had a very similar
>> I propose a refactor of those functions, given that I need to create a
>> similar one for this patchset.
>
> The diff here is pretty hard (for me) to review; I'll need more time
> to check it. What might make review easier (at least for me), is to
> incrementally change these routines. i.e. separate patches to:
>
> - add the new infrastructure
> - replace e820__range_remove
> - replace __e820__range_update
>
> If that's not actually useful, no worries. I'll just stare at it a bit
> more. :)
>

Yep, that's a good idea. I'll keep that in mind for the next patch.

>>
>> Add a function to modify a E820 table in a given range. This
>> modification is done backed up by two helper structs:
>> e820_entry_updater and e820_*_data.
>>
>> The first one, e820_entry_updater, carries 3 callbacks which function
>> as the actions to take on the table.
>>
>> The other one, e820_*_data carries information needed by the
>> callbacks, for example in the case of range_update it will carry the
>> type that we are targeting.
>
> Something I think would be really amazing here is if you could add KUnit
> tests here to exercise the corner cases and validate the changes. It
> should be pretty easy to add. Here's a quick example for the boilerplate
> and testing a bit of __e820__range_add():
>
> #ifdef CONFIG_E820_KUNIT_TEST
> #include <kunit/test.h>
>
> static void __init test_e820_range_add(struct kunit *context)
> {
> 	struct e820_table table;
> 	u32 full;
>
> 	full = ARRAY_SIZE(table.entries);
> 	/* Add last entry. */
> 	table->nr_entries = full - 1;
> 	__e820__range_add(&table, 0, 15, 0);
> 	KUNIT_EXPECT_EQ(table->nr_entries, full)
> 	/* Skip new entry when full. */
> 	__e820__range_add(&table, 0, 15, 0);
> 	KUNIT_EXPECT_EQ(table->nr_entries, full)
> }
>
> static void __init test_e820_update(struct kunit *context)
> {
> ...
> }
>
> static struct kunit_case __refdata e820_test_cases[] = {
>         KUNIT_CASE(test_e820_range_add),
>         KUNIT_CASE(test_e820_update),
> 	...
>         {}
> };
>
> static struct kunit_suite e820_test_suite = {
>         .name = "e820",
>         .test_cases = e820_test_cases,
> };
>
> kunit_test_suites(&e820_test_suite);
> #endif
>

Oh that's awesome! I'll definitely take a look into KUnit and integrate
it to this patch. Thanks for the code snippet!