linux-kernel - Re: [PATCH v3 00/30] Live Update Orchestrator

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Message-ID: <20250826162203.GE2130239@nvidia.com>
Date: Tue, 26 Aug 2025 13:22:03 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Pasha Tatashin <pasha.tatashin@...een.com>
Cc: Pratyush Yadav <pratyush@...nel.org>, jasonmiu@...gle.com,
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Subject: Re: [PATCH v3 00/30] Live Update Orchestrator

On Tue, Aug 26, 2025 at 04:10:31PM +0000, Pasha Tatashin wrote:
> 
> > I think in the calls the idea was it was reasonable to start without
> > sessions fds at all, but in this case we shouldn't be mucking with
> > pids or current.
> 
> The existing interface, with the addition of passing a pidfd, provides
> the necessary flexibility without being invasive. The change would be
> localized to the new code that performs the FD retrieval and wouldn't
> involve spoofing current or making widespread changes.
> For example, to handle cgroup charging for a memfd, the flow inside
> memfd_luo_retrieve() would look something like this:
> 
> task = get_pid_task(target_pid, PIDTYPE_PID);
> mm = get_task_mm(task);
>     // ...
>     folio = kho_restore_folio(phys);
>     // Charge to the target mm, not 'current->mm'
>     mem_cgroup_charge(folio, mm, ...);
> mmput(mm);
> put_task_struct(task);

Execpt it doesn't work like that in all places, iommufd for example
uses GFP_KERNEL_ACCOUNT which relies on current.

How you fix that when current is the wrong cgroup, I have no idea if
it is even possible.

Jason