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Date: Mon, 28 Sep 2015 14:17:46 -0600 From: Al Stone <ahs3@...hat.com> To: "Rafael J. Wysocki" <rjw@...ysocki.net>, Al Stone <al.stone@...aro.org> Cc: linux-acpi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org, linux-pm@...r.kernel.org, linaro-acpi@...ts.linaro.org, linaro-kernel@...ts.linaro.org, patches@...aro.org Subject: Re: [PATCH v4 0/5] Provide better MADT subtable sanity checks On 09/25/2015 05:29 PM, Rafael J. Wysocki wrote: > On Wednesday, September 16, 2015 05:26:40 PM Al Stone wrote: >> Currently, the BAD_MADT_ENTRY macro is used to do a very simple sanity >> check on the various subtables that are defined for the MADT. The check >> compares the size of the subtable data structure as defined by ACPICA to >> the length entry in the subtable. If they are not the same, the assumption >> is that the subtable is incorrect. >> >> Over time, the ACPI spec has allowed for MADT subtables where this can >> never be true (the local SAPIC subtable, for example). Or, more recently, >> the spec has accumulated some minor flaws where there are three possible >> sizes for a subtable, all of which are valid, but only for specific versions >> of the spec (the GICC subtable). In both cases, BAD_MADT_ENTRY reports these >> subtables as bad when they are not. In order to retain some sanity check >> on the MADT subtables, we now have to special case these subtables. Of >> necessity, these special cases have ended up in arch-dependent code (arm64) >> or an arch has simply decided to forgo the check (ia64). >> >> This patch set replaces the BAD_MADT_ENTRY macro with a function called >> bad_madt_entry(). This function uses a data set of details about the >> subtables to provide more sanity checking than before: >> >> -- is the subtable legal for the version given in the FADT? >> >> -- is the subtable legal for the revision of the MADT in use? >> >> -- is the subtable of the proper length (including checking >> on the one variable length subtable that is currently ignored), >> given the FADT version and the MADT revision? >> >> Further, this patch set adds in the call to bad_madt_entry() from the >> acpi_table_parse_madt() function, allowing it to be used consistently >> by all architectures, for all subtables, and removing the need for each >> of the subtable traversal callback functions to use BAD_MADT_ENTRY. >> >> In theory, as the ACPI specification changes, we would only have to add >> additional information to the data set describing the MADT subtables in >> order to continue providing sanity checks, even when new subtables are >> added. >> >> These patches have been tested on an APM Mustang (arm64) and are known to >> work there. They have also been cross-compiled for x86 and ia64 with no >> known failures. >> >> Changes for v4: >> -- Remove extraneous white space change (Graeme Gregory) >> -- acpi_parse_entries() changes also needed a check to make sure that >> only MADT entries used bad_madt_entry() (Sudeep Holla) >> -- inadvertent use of 01day build noted that bad_madt_entry() can be >> static, so added it (Sudeep Holla, Fengguang Wu) >> >> Changes for v3: >> -- Reviewed-and-tested-by from Sudeep Holla for arm64 parts >> -- Clearer language in error messages (Graeme Gregory, Timur Tabi) >> -- Double checked that inserting call to bad_madt_entry() into the >> function acpi_parse_entries() does not impact current behavior >> (Sudeep Holla) >> >> Changes for v2: >> -- Acked-by on 2/5 from Marc Zyngier and Catalin Marinas for ARM >> -- Correct faulty end of loop test found by Timur Tabi >> >> >> Al Stone (5): >> ACPI: add in a bad_madt_entry() function to eventually replace the >> macro >> ACPI / ARM64: remove usage of BAD_MADT_ENTRY/BAD_MADT_GICC_ENTRY >> ACPI / IA64: remove usage of BAD_MADT_ENTRY >> ACPI / X86: remove usage of BAD_MADT_ENTRY >> ACPI: remove definition of BAD_MADT_ENTRY macro > > I've queued this up for v4.4, but I had to rebase it on top of some previous > changes in my linux-next branch. > > Can you please look at my bleeding-edge branch and see if the result of the > rebase is as intended? In particular, I'm not sure if we really need to return > -EINVAL from acpi_parse_entries_array() when we find a bad MADT entry or it > will be sufficient to simply go to the next entry in that case? > > Thanks, > Rafael I see there being two options: (1) return -EINVAL and indicate that the tables are incorrect, or (2) print a warning (or something more aggressive?), go to the next entry, and hope for the best with the remainder of the MADT subtables. The former is consistent with past behavior, I think, and the latter seems to me a bit of a gamble. So, my vote is for (1), the current method; what are you thinking these days? -- ciao, al ----------------------------------- Al Stone Software Engineer Red Hat, Inc. ahs3@...hat.com ----------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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