From mboxrd@z Thu Jan 1 00:00:00 1970 From: Khalid Aziz Subject: [RFC PATCH v7 16/16] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) Date: Thu, 10 Jan 2019 14:09:48 -0700 Message-Id: In-Reply-To: References: In-Reply-To: References: To: juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de, ak@linux.intel.com, torvalds@linux-foundation.org, liran.alon@oracle.com, keescook@google.com, konrad.wilk@oracle.com Cc: Khalid Aziz , deepa.srinivasan@oracle.com, chris.hyser@oracle.com, tyhicks@canonical.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com, jcm@redhat.com, boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com, joao.m.martins@oracle.com, jmattson@google.com, pradeep.vincent@oracle.com, john.haxby@oracle.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de, steven.sistare@oracle.com, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: XPFO flushes kernel space TLB entries for pages that are now mapped in userspace on not only the current CPU but also all other CPUs. If the number of TLB entries to flush exceeds tlb_single_page_flush_ceiling, this results in entire TLB neing flushed on all CPUs. A malicious userspace app can exploit the dual mapping of a physical page caused by physmap only on the CPU it is running on. There is no good reason to incur the very high cost of TLB flush on CPUs that may never run the malicious app or do not have any TLB entries for the malicious app. The cost of full TLB flush goes up dramatically on machines with high core count. This patch flushes relevant TLB entries for current process or entire TLB depending upon number of entries for the current CPU and posts a pending TLB flush on all other CPUs when a page is unmapped from kernel space and mapped in userspace. This pending TLB flush is posted for each task separately and TLB is flushed on a CPU when a task is scheduled on it that has a pending TLB flush posted for that CPU. This patch does two things - (1) it potentially aggregates multiple TLB flushes into one, and (2) it avoids TLB flush on CPUs that never run the task that caused a TLB flush. This has very significant impact especially on machines with large core counts. To illustrate this, kernel was compiled with -j on two classes of machines - a server with high core count and large amount of memory, and a desktop class machine with more modest specs. System time from "make -j" from vanilla 4.20 kernel, 4.20 with XPFO patches before applying this patch and after applying this patch are below: Hardware: 96-core Intel Xeon Platinum 8160 CPU @ 2.10GHz, 768 GB RAM make -j60 all 4.20 915.183s 4.19+XPFO 24129.354s 26.366x 4.19+XPFO+Deferred flush 1216.987s 1.330xx Hardware: 4-core Intel Core i5-3550 CPU @ 3.30GHz, 8G RAM make -j4 all 4.20 607.671s 4.19+XPFO 1588.646s 2.614x 4.19+XPFO+Deferred flush 794.473s 1.307xx This patch could use more optimization. For instance, it posts a pending full TLB flush for other CPUs even when number of TLB entries being flushed does not exceed tlb_single_page_flush_ceiling. Batching more TLB entry flushes, as was suggested for earlier version of these patches, can help reduce these cases. This same code should be implemented for other architectures as well once finalized. Signed-off-by: Khalid Aziz --- arch/x86/include/asm/tlbflush.h | 1 + arch/x86/mm/tlb.c | 27 +++++++++++++++++++++++++++ arch/x86/mm/xpfo.c | 2 +- include/linux/sched.h | 9 +++++++++ 4 files changed, 38 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h index f4204bf377fc..92d23629d01d 100644 --- a/arch/x86/include/asm/tlbflush.h +++ b/arch/x86/include/asm/tlbflush.h @@ -561,6 +561,7 @@ extern void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start, unsigned long end, unsigned int stride_shift, bool freed_tables); extern void flush_tlb_kernel_range(unsigned long start, unsigned long end); +extern void xpfo_flush_tlb_kernel_range(unsigned long start, unsigned long end); static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a) { diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 03b6b4c2238d..b04a501c850b 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -319,6 +319,15 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, __flush_tlb_all(); } #endif + + /* If there is a pending TLB flush for this CPU due to XPFO + * flush, do it now. + */ + if (tsk && cpumask_test_and_clear_cpu(cpu, &tsk->pending_xpfo_flush)) { + count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED); + __flush_tlb_all(); + } + this_cpu_write(cpu_tlbstate.is_lazy, false); /* @@ -801,6 +810,24 @@ void flush_tlb_kernel_range(unsigned long start, unsigned long end) } } +void xpfo_flush_tlb_kernel_range(unsigned long start, unsigned long end) +{ + + /* Balance as user space task's flush, a bit conservative */ + if (end == TLB_FLUSH_ALL || + (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) { + do_flush_tlb_all(NULL); + } else { + struct flush_tlb_info info; + + info.start = start; + info.end = end; + do_kernel_range_flush(&info); + } + cpumask_setall(¤t->pending_xpfo_flush); + cpumask_clear_cpu(smp_processor_id(), ¤t->pending_xpfo_flush); +} + void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) { struct flush_tlb_info info = { diff --git a/arch/x86/mm/xpfo.c b/arch/x86/mm/xpfo.c index bcdb2f2089d2..5aa17cb2c813 100644 --- a/arch/x86/mm/xpfo.c +++ b/arch/x86/mm/xpfo.c @@ -110,7 +110,7 @@ inline void xpfo_flush_kernel_tlb(struct page *page, int order) return; } - flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size); + xpfo_flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * size); } /* Convert a user space virtual address to a physical address. diff --git a/include/linux/sched.h b/include/linux/sched.h index 291a9bd5b97f..ba298be3b5a1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1206,6 +1206,15 @@ struct task_struct { unsigned long prev_lowest_stack; #endif + /* + * When a full TLB flush is needed to flush stale TLB entries + * for pages that have been mapped into userspace and unmapped + * from kernel space, this TLB flush will be delayed until the + * task is scheduled on that CPU. Keep track of CPUs with + * pending full TLB flush forced by xpfo. + */ + cpumask_t pending_xpfo_flush; + /* * New fields for task_struct should be added above here, so that * they are included in the randomized portion of task_struct. -- 2.17.1