On Fri, Sep 10, 2021 at 12:12 PM Jann Horn <jannh@xxxxxxxxxx> wrote: > > On Fri, Sep 10, 2021 at 6:28 PM Peter Oskolkov <posk@xxxxxxxxxx> wrote: > > On Fri, Sep 10, 2021 at 9:13 AM Prakash Sangappa > > <prakash.sangappa@xxxxxxxxxx> wrote: > > > > Do you think your sys_task_getshared can be tweaked to return an > > > > arbitrarily-sized block of memory (subject to overall constraints) > > > > rather than a fixed number of "options"? > > > > > > I suppose it could. How big of a size? We don’t want to hold on to > > > arbitrarily large amount of pinned memory. The preference would > > > be for the kernel to decide what is going to be shared based on > > > what functionality/data sharing is supported. In that sense the size > > > is pre defined not something the userspace/application can ask. > > > > There could be a sysctl or some other mechanism that limits the amount > > of memory pinned per mm (or per task). Having "options" hardcoded for > > such a generally useful feature seems limiting... > > That seems like it'll just create trouble a few years down the line > when the arbitrarily-chosen limit that nobody is monitoring blows up > in someone's production environment. > > If this area is used for specific per-thread items, then the kernel > should be able to enforce that you only allocate as much space as is > needed for all threads of the process (based on the maximum number > that have ever been running in parallel in the process), right? Which > would probably work best if the kernel managed those allocations. This sounds, again, as if the kernel should be aware of the kind of items being allocated; having a more generic mechanism of allocating pinned memory for the userspace to use at its discretion would be more generally useful, I think. But how then the kernel/system should be protected from a buggy or malicious process trying to grab too much? One option would be to have a generic in-kernel mechanism for this, but expose it to the userspace via domain-specific syscalls that do the accounting you hint at. This sounds a bit like an over-engineered solution, though...
