Thanks a lot for the reply, Steve. However, my question is not about what happens after process exit. I agree that the memory associated with the process will be freed after exit and this makes it's TLB entries stale.
What I am looking for is what happens after process switch, when scheduler switches out one process. One of the possible reasons for this is expired time slice.
In this case, memory mapping for the switched out process is still valid as long as the correct Page Global Directory is used. Also, since TLB holds translation entries with respect to this memory mapping, these entries are valid one. But still, CR3 is rewritten which flushes out these valid entries. This is necessary just because linux uses different Page Global Directory for each process as stated in my earlier post.
I have also seen ASID parameter for flushing macros in linux source, but not sure how and where it is used. Please let me know more on this. Hi Finally, I got the answer for this. Hence there is no way to distinguish TLB Entries of one process from other. Please correct me if this is wrong. Some more questions on the same line. I have read that linux uses only 48 bits out of 64 on bit intel processors. Does it mean that remaining bits can be used to emulate Tagged TLB i.
Do someone know what can be the reason behind not implementing Tagged TLB by Intel even on VT when it has been proved that its much beneficial for Virtual machines? Thanks in advance. The Linux kernel has many different types of TLB-related functions which it calls at various times, and these functions are designed to have the potential of being very specific. Each processor's implementation of those functions varies according to what a particular engine or model can do.
In some cases, like "Motorola with no MMU," they don't do anything at all. When a task-switch occurs, the new task does not know anything about the old task. It will soon fill-up the TLB with the entries that it cares about, having no real need for and probably, no access to those of the former task. Find More Posts by sundialsvcs View Blog.
Originally Posted by sundialsvcs. Interesting topic - although I wonder about all this conjecture. Just this last week I was quickly skimming some of the code tangentially related this to see how the swap pte's were handled with regard to new reporting being added to smaps. It appeared from the code that normally only the TLB entries for the task interrupted were being invalidated, rather than a full TLB flush. TLB Flush.
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Hi, I am starting to wonder whether I understood the synchronisation points e. According to the specification 3 should not be necessary: Note that writing satp does not imply any ordering constraints between page-table updates and subsequent address translations.
Hesham Almatary. On the 80 x 86 architecture, this function forces every CPU to invalidate all local TLB entries relative to nonglobal pages of the specified set of Page Tables. Invalidates all TLB entries of the nonglobal pages in a specified address range of a given set of Page Tables. On the 80 x 86 architecture, this macro is equivalent to flush tlb mm. To do this, the kernel temporarily clears the PGE flag in cr4 and then writes into the cr3 register. In fact, each kernel thread does not have its own set of Page Tables; rather, it makes use of the set of Page Tables belonging to a regular process.
However, there is no need to invalidate a TLB entry that refers to a User Mode linear address because no kernel thread accesses the User Mode address space.
Continue reading here: TLB mode mechanism it is usually invoked whenever the kernel modifies a Page Table entry relative to the Kernel Mode address space.
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