Init module: flush_dcache
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src/aarch64-linux-flush-dcache/.vscode-ctags
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src/aarch64-linux-flush-dcache/.vscode-ctags
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44
src/aarch64-linux-flush-dcache/.vscode/c_cpp_properties.json
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src/aarch64-linux-flush-dcache/.vscode/c_cpp_properties.json
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10
src/aarch64-linux-flush-dcache/.vscode/settings.json
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src/aarch64-linux-flush-dcache/.vscode/settings.json
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97
src/aarch64-linux-flush-dcache/mod_entry.c
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src/aarch64-linux-flush-dcache/mod_entry.c
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#include <asm-generic/cacheflush.h>
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#include <linux/irqflags.h>
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#include <linux/mm_types.h>
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#include <linux/mmap_lock.h>
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#include <linux/mm.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/module.h>
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/* PID: The task for which page cache is to be flushed. */
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static int param_pid;
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module_param_named(pid, param_pid, int, 0644);
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/* addr: The virtual memory address used to index into the page to be flushed. */
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static unsigned long param_vmaddr;
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module_param_named(addr, param_vmaddr, ulong, 0644);
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static int __init flush_dcache_init(void)
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{
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struct task_struct *tsk;
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struct mm_struct *mm_of_tsk;
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struct page *page_of_addr;
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// Get task_struct from PID, then get its mm_struct
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rcu_read_lock();
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tsk = find_task_by_pid_ns(param_pid, &init_pid_ns);
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if (!tsk) {
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rcu_read_unlock();
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goto ret_err_no_tsk;
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}
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mm_of_tsk = get_task_mm(tsk);
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rcu_read_unlock();
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// No mm_struct -- may be kthread?
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if (!mm_of_tsk)
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goto ret_warn_kthread;
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/* Get page from mm_struct --
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* We need to pin the page i.e., have it marked as FOLL_PIN.
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* Ref. Documentation/core-api/pin_user_pages.rst:
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* Because we are writing to the data represented by the page -- we are
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* flushing cache to dirty page, after all -- we need FOLL_PIN instead
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* of *get-API. This effectively? prevents page from being evicted in
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* the short term.
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*/
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mmap_read_lock(mm_of_tsk);
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long pin_pages_retval = pin_user_pages_remote(
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mm_of_tsk, param_vmaddr, 1,
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FOLL_WRITE, &page_of_addr, NULL
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); // We know mmap is locked, stop asking.
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if (pin_pages_retval != 1) {
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mmap_read_unlock(mm_of_tsk);
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goto ret_err_no_page;
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}
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// Begin test. We ABSOLUTELY cannot be interrupted here...
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unsigned long _eflags;
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local_irq_save(_eflags);
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// [TODO]: Use non-temporal instr to write directly to memory.
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// This will most certainly require asm blocks...
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// ...Or else, simulate a cache-incoherent DMA?
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// e.g., run in qemu -> attach gdb on vmlinux -> breakpoint ->
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// gdb examines physical mem -> gdb makes a silly write ->
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// continue, check here.
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// ...Or else, pgprot_noncached
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pr_info("Before flush: cache line/memory diff: ");
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flush_dcache_page(page_of_addr);
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pr_info("After flush: ...");
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mmap_read_unlock(mm_of_tsk);
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local_irq_restore(_eflags);
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unpin_user_pages(&page_of_addr, 1);
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return 0;
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ret_warn_kthread:
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pr_warn("[%s] Cannot find `tsk->mm` for PID %d. This may be a kthread.\n"
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"Messing with `active_mm` may be unsafe. Exiting...",
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__func__, param_pid);
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return 0;
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ret_err_no_tsk:
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pr_err("[%s] Cannot find `task_struct` for PID %d.",
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__func__, param_pid);
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return -EINVAL;
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ret_err_no_page:
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pr_err("[%s] Cannot pin requested pages. [TODO]", __func__);
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return pin_pages_retval == 0 ? -EINVAL : (int)pin_pages_retval;
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}
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static void __exit flush_dcache_exit(void)
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{
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pr_info("[%s] See ya~", __func__);
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}
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module_init(flush_dcache_init);
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module_exit(flush_dcache_exit);
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MODULE_LICENSE("GPL");
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