> On Sep 10, 2021, at 12:36 PM, Peter Oskolkov <posk@xxxxxxxxxx> wrote: > > 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… What will this pinned memory be used for in your use case, can you explain?
