Re: [PATCH v3 0/5] of: reserved_mem: several fixes about reserved memory

[Marek Szyprowski]

On 03.10.2026 10:04, Mike Rapoport wrote:
> On Tue, Sep 22, 2026 at 05:24:32PM +0800, Wandun wrote:
>> On 9/22/26 16:48, Mike Rapoport wrote:
>>> On Sun, Sep 20, 2026 at 05:28:47PM +0800, Wandun Chen wrote:
>>>> From: Wandun Chen <chenwandun@xxxxxxxxxxx>
>>>>
>>>> This series fixes several error-handling issues in the reserved-memory
>>>> initialization paths.
>>>>
>>>> The first two patches fix cleanup of no-map regions after driver
>>>> initialization failure.
>>>>
>>>> Static reserved-memory nodes are reserved during the early DT scan but
>>>> initialized later. The third patch tags regions whose early reservation
>>>> succeeded, so the late scan can skip the nodes whose early reservation
>>>> failed.
>>>>
>>>> The last two patches reject overlapping static regions. Without
>>>> these checks, overlapping nodes can be initialized over the same
>>>> physical memory, result in data corrupt.
>>>>
>>>> Sashiko reported these issues in [1] [2] [3].
>>>>
>>>> [1] https://protect2.fireeye.com/v1/url?k=7e2f7441-1fa46164-7e2eff0e-74fe485cbff6-619f01488e6b7010&q=1&e=f3c07e6c-275b-4aa1-aec1-d931cda5f11a&u=https%3A%2F%2Fsashiko.dev%2F%23%2Fmessage%2F20260814090305.4C8741F00A3D%2540smtp.kernel.org
>>>> [2] https://protect2.fireeye.com/v1/url?k=a92ba57b-c8a0b05e-a92a2e34-74fe485cbff6-5f58f4b0f32080b9&q=1&e=f3c07e6c-275b-4aa1-aec1-d931cda5f11a&u=https%3A%2F%2Fsashiko.dev%2F%23%2Fmessage%2F20260814084718.29C341F000E9%2540smtp.kernel.org
>>>> [3] https://protect2.fireeye.com/v1/url?k=4f58aae4-2ed3bfc1-4f5921ab-74fe485cbff6-f4c4b3d0ed61b93e&q=1&e=f3c07e6c-275b-4aa1-aec1-d931cda5f11a&u=https%3A%2F%2Fsashiko.dev%2F%23%2Fmessage%2F20260806100605.2C2C01F000E9%2540smtp.kernel.org
>>>>
>>>> v2 --> v3:
>>>> 1. Rework the mechanism that checks in the late scan whether the early
>>>>    reservation succeeded (patches 3-5, suggested by Marek, thanks).
>>>>
>>>>    Patch 3 adds a new memblock flag MEMBLOCK_RSRV_RMEM, which is set when
>>>>    the early reservation of a static region succeeds and checked in the
>>>>    late scan.
>>> Can we keep this local to of_reserved_mem please?
>> Probably not. I do not see a way to keep this entirely local to
>> of_reserved_mem while handling the issue robustly.
>>
>> I previously implemented an approach in of_reserved_mem that records
>> static reserved-memory nodes whose early reservation failed in a local
>> array [1]. However, the early scan runs before paging_init(), so the array
>> cannot be dynamically expanded. If the number of failed nodes exceeds
>> the array size, some failures cannot be recorded and the issue remains,
>> and that is why Marek said "partial solution", although in practice
>> having that many failed nodes is unlikely.
> Even before paging_init() there is memblock_alloc().

One can call it, but such memory cannot be dereferenced/accessed for example
on ARM64, because it is not yet mapped in the linear map.

>> To handle this robustly, the late scan needs a way to determine whether
>> the corresponding early reservation actually succeeded. Current approach
>> uses memblock to retain that state.
> I can't say I like the idea of keeping this state in memblock.
> This add flags and code to memblock to deal with corner cases of bad
> firmware that reports weird memory layouts, and once there is a flag in
> the common infrastructure, people tend to abuse it.

So far I found no better place to store the information about successful
region reservation.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland