[PATCH v2 18/63] drm/amd/pm: Use struct_group() for memcpy() region
Lazar, Lijo
lijo.lazar at amd.com
Thu Aug 19 05:03:43 UTC 2021
On 8/19/2021 5:29 AM, Kees Cook wrote:
> On Wed, Aug 18, 2021 at 05:12:28PM +0530, Lazar, Lijo wrote:
>>
>> On 8/18/2021 11:34 AM, Kees Cook wrote:
>>> In preparation for FORTIFY_SOURCE performing compile-time and run-time
>>> field bounds checking for memcpy(), memmove(), and memset(), avoid
>>> intentionally writing across neighboring fields.
>>>
>>> Use struct_group() in structs:
>>> struct atom_smc_dpm_info_v4_5
>>> struct atom_smc_dpm_info_v4_6
>>> struct atom_smc_dpm_info_v4_7
>>> struct atom_smc_dpm_info_v4_10
>>> PPTable_t
>>> so the grouped members can be referenced together. This will allow
>>> memcpy() and sizeof() to more easily reason about sizes, improve
>>> readability, and avoid future warnings about writing beyond the end of
>>> the first member.
>>>
>>> "pahole" shows no size nor member offset changes to any structs.
>>> "objdump -d" shows no object code changes.
>>>
>>> Cc: "Christian König" <christian.koenig at amd.com>
>>> Cc: "Pan, Xinhui" <Xinhui.Pan at amd.com>
>>> Cc: David Airlie <airlied at linux.ie>
>>> Cc: Daniel Vetter <daniel at ffwll.ch>
>>> Cc: Hawking Zhang <Hawking.Zhang at amd.com>
>>> Cc: Feifei Xu <Feifei.Xu at amd.com>
>>> Cc: Lijo Lazar <lijo.lazar at amd.com>
>>> Cc: Likun Gao <Likun.Gao at amd.com>
>>> Cc: Jiawei Gu <Jiawei.Gu at amd.com>
>>> Cc: Evan Quan <evan.quan at amd.com>
>>> Cc: amd-gfx at lists.freedesktop.org
>>> Cc: dri-devel at lists.freedesktop.org
>>> Signed-off-by: Kees Cook <keescook at chromium.org>
>>> Acked-by: Alex Deucher <alexander.deucher at amd.com>
>>> Link: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2FCADnq5_Npb8uYvd%2BR4UHgf-w8-cQj3JoODjviJR_Y9w9wqJ71mQ%40mail.gmail.com&data=04%7C01%7Clijo.lazar%40amd.com%7C3861f20094074bf7328808d962a433f2%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637649279701053991%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=386LcfJJGfQfHsXBuK17LMqxJ2nFtGoj%2FUjoN2ZtJd0%3D&reserved=0
>>> ---
>>> drivers/gpu/drm/amd/include/atomfirmware.h | 9 ++++++++-
>>> .../gpu/drm/amd/pm/inc/smu11_driver_if_arcturus.h | 3 ++-
>>> drivers/gpu/drm/amd/pm/inc/smu11_driver_if_navi10.h | 3 ++-
>>> .../gpu/drm/amd/pm/inc/smu13_driver_if_aldebaran.h | 3 ++-
>>
>> Hi Kees,
>
> Hi! Thanks for looking into this.
>
>> The headers which define these structs are firmware/VBIOS interfaces and are
>> picked directly from those components. There are difficulties in grouping
>> them to structs at the original source as that involves other component
>> changes.
>
> So, can you help me understand this a bit more? It sounds like these are
> generated headers, yes? I'd like to understand your constraints and
> weight them against various benefits that could be achieved here.
>
> The groupings I made do appear to be roughly documented already,
> for example:
>
> struct atom_common_table_header table_header;
> // SECTION: BOARD PARAMETERS
> + struct_group(dpm_info,
>
> Something emitted the "BOARD PARAMETERS" section heading as a comment,
> so it likely also would know where it ends, yes? The good news here is
> that for the dpm_info groups, they all end at the end of the existing
> structs, see:
> struct atom_smc_dpm_info_v4_5
> struct atom_smc_dpm_info_v4_6
> struct atom_smc_dpm_info_v4_7
> struct atom_smc_dpm_info_v4_10
>
> The matching regions in the PPTable_t structs are similarly marked with a
> "BOARD PARAMETERS" section heading comment:
>
> --- a/drivers/gpu/drm/amd/pm/inc/smu11_driver_if_arcturus.h
> +++ b/drivers/gpu/drm/amd/pm/inc/smu11_driver_if_arcturus.h
> @@ -643,6 +643,7 @@ typedef struct {
> // SECTION: BOARD PARAMETERS
>
> // SVI2 Board Parameters
> + struct_group(v4_6,
> uint16_t MaxVoltageStepGfx; // In mV(Q2) Max voltage step that SMU will request. Multiple steps are taken if voltage change exceeds this value.
> uint16_t MaxVoltageStepSoc; // In mV(Q2) Max voltage step that SMU will request. Multiple steps are taken if voltage change exceeds this value.
>
> @@ -728,10 +729,10 @@ typedef struct {
> uint32_t BoardVoltageCoeffB; // decode by /1000
>
> uint32_t BoardReserved[7];
> + );
>
> // Padding for MMHUB - do not modify this
> uint32_t MmHubPadding[8]; // SMU internal use
> -
> } PPTable_t;
>
> Where they end seems known as well (the padding switches from a "Board"
> to "MmHub" prefix at exactly the matching size).
>
> So, given that these regions are already known by the export tool, how
> about just updating the export tool to emit a struct there? I imagine
> the problem with this would be the identifier churn needed, but that's
> entirely mechanical.
>
> However, I'm curious about another aspect of these regions: they are,
> by definition, the same. Why isn't there a single struct describing
> them already, given the existing redundancy? For example, look at the
> member names: maxvoltagestepgfx vs MaxVoltageStepGfx. Why aren't these
> the same? And then why aren't they described separately?
>
> Fixing that would cut down on the redundancy here, and in the renaming,
> you can fix the identifiers as well. It should be straight forward to
> write a Coccinelle script to do this renaming for you after extracting
> the structure.
>
>> The driver_if_* files updates are frequent and it is error prone to manually
>> group them each time we pick them for any update.
>
> Why are these structs updated? It looks like they're specifically
> versioned, and aren't expected to change (i.e. v4.5, v4.6, v4.10, etc).
>
>> Our usage of memcpy in this way is restricted only to a very few places.
>
> True, there's 1 per PPTable_t duplication. With a proper struct, you
> wouldn't even need a memcpy().
>
> Instead of the existing:
> memcpy(smc_pptable->I2cControllers, smc_dpm_table_v4_7->I2cControllers,
> sizeof(*smc_dpm_table_v4_7) - sizeof(smc_dpm_table_v4_7->table_header));
>
> or my proposed:
> memcpy(&smc_pptable->v4, &smc_dpm_table_v4_7->dpm_info,
> sizeof(smc_dpm_table_v4_7->dpm_info));
>
> you could just have:
> smc_pptable->v4 = smc_dpm_table_v4_7->dpm_info;
>
> since they'd be explicitly the same type.
>
> That looks like a much cleaner solution to this. It greatly improves
> readability, reduces the redundancy in the headers, and should be a
> simple mechanical refactoring.
>
> Oh my, I just noticed append_vbios_pptable() in
> drivers/gpu/drm/amd/pm/powerplay/hwmgr/vega12_processpptables.c
> which does an open-coded assignment of the entire PPTable_t, including
> padding, and, apparently, the i2c address twice:
>
> ppsmc_pptable->Vr2_I2C_address = smc_dpm_table.Vr2_I2C_address;
>
> ppsmc_pptable->Vr2_I2C_address = smc_dpm_table.Vr2_I2C_address;
>
>> As another option - is it possible to have a helper function/macro like
>> memcpy_fortify() which takes the extra arguments and does the extra compile
>> time checks? We will use the helper whenever we have such kind of usage.
>
> I'd rather avoid special cases just for this, especially when the code
> here is already doing a couple things we try to avoid in the rest of
> the kernel (i.e. open coded redundant struct contents, etc).
>
> If something mechanically produced append_vbios_pptable() above, I bet
> we can get rid of the memcpy()s entirely and save a lot of code doing a
> member-to-member assignment.
>
> What do you think?
>
Hi Kees,
Will give a background on why there are multiple headers and why it's
structured this way. That may help to better understand this arrangement.
This code is part of driver for AMD GPUs. These GPUs get to the
consumers through multiple channels - AMD designs a few boards with
those, there are add-in-board partners like ASRock, Sapphire etc. who
take these ASICs and design their own boards, and others like OEM
vendors who have their own design for boards in their laptops.
As you have noticed, this particular section in the structure carries
information categorized as 'BOARD PARAMETERS'. Since there are multiple
vendors designing their own boards, this gives the option to customize
the parameters based on their board design.
There are a few components in AMD GPUs which are interested in these
board parameters main ones being - Video BIOS (VBIOS) and power
management firmware (PMFW). There needs to be a single source where a
vendor can input the information and that is decided as VBIOS. VBIOS
carries different data tables which carry other information also (some
of which are used by driver), so this information is added as a separate
data table in VBIOS. A board vendor can customize the VBIOS build with
this information.
The data tables (and some other interfaces with driver) carried by VBIOS
are published in this header - drivers/gpu/drm/amd/include/atomfirmware.h
There are multiple families of AMD GPUs like Navi10, Arcturus, Aldebaran
etc. and the board specific details change with different families of
GPUs. However, VBIOS team publishes a common header file for these GPUs
and any difference in data tables (between GPU families) is maintained
through a versioning scheme. Thus there are different tables like
atom_smc_dpm_info_v4_5, atom_smc_dpm_info_v4_6 etc. which are relevant
for a particular family of GPUs.
With newer VBIOS versions and new GPU families, there could be changes
in the structs defined in atomfirmware.h and we pick the header accordingly.
As mentioned earlier, one other user of the board specific information
is power management firmware (PMFW). PMFW design is isolated from the
actual source of board information. In addition to board specific
information, PMFW needs some other info as well and driver is the one
responsible for passing this info to the firmware. PMFW gives an
interface header to driver providing the different struct formats which
are used in driver<->PMFW interactions. Unlike VBIOS, these interface
headers are defined per family of ASICs and those are
smu11_driver_if_arcturus.h, smu11_driver_if_* etc. (in short driver_if_*
files). Like VBIOS, with newer firmware versions, there could be
changes in the different structs defined in these headers and we pick
them accordingly.
Driver acts the intermediary between actual source of board information
(VBIOS) and PMFW. So what is being done here is driver picks the board
information from VBIOS table, strips the VBIOS table header and passes
it as part of PPTable_t which defines all the information that is needed
by PMFW from driver for enabling dynamic power management.
In summary, these headers are not generated and not owned by driver.
They define the interfaces of two different components with driver, and
are consumed by those components themselves. A simple change to group
the information as a separate structure involves changes in multiple
components like VBIOS, PMFW, software used to build VBIOS, Windows
driver etc.
In all practical cases, this code is harmless as these structs (in both
headers) are well defined for a specific family of GPUs. There is always
a reserve field defined with some extra bytes so that the size is not
affected if at all new fields need to be added.
The patch now makes us to modify the headers for Linux through
script/manually whenever we pick them, and TBH that strips off the
coherency with the original source. The other option is field by field
copy. Now we use memcpy as a safe bet so that a new field added later
taking some reserve space is not missed even if we miss a header update.
Thanks,
Lijo
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