From 948084f0f6959f602f89f679522b706a72da0285 Mon Sep 17 00:00:00 2001 From: "Fabio M. De Francesco" Date: Sun, 21 Aug 2022 20:25:19 +0200 Subject: [PATCH] kexec: replace kmap() with kmap_local_page() kmap() is being deprecated in favor of kmap_local_page(). There are two main problems with kmap(): (1) It comes with an overhead as mapping space is restricted and protected by a global lock for synchronization and (2) it also requires global TLB invalidation when the kmap's pool wraps and it might block when the mapping space is fully utilized until a slot becomes available. With kmap_local_page() the mappings are per thread, CPU local, can take page faults, and can be called from any context (including interrupts). It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, the tasks can be preempted and, when they are scheduled to run again, the kernel virtual addresses are restored and are still valid. Since its use in kexec_core.c is safe everywhere, it should be preferred. Therefore, replace kmap() with kmap_local_page() in kexec_core.c. Tested on a QEMU/KVM x86_32 VM, 6GB RAM, booting a kernel with HIGHMEM64GB enabled. Link: https://lkml.kernel.org/r/20220821182519.9483-1-fmdefrancesco@gmail.com Signed-off-by: Fabio M. De Francesco Suggested-by: Ira Weiny Reviewed-by: Ira Weiny Acked-by: Baoquan He Signed-off-by: Andrew Morton --- kernel/kexec_core.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c index 5ca4d40c9ec1..ca2743f9c634 100644 --- a/kernel/kexec_core.c +++ b/kernel/kexec_core.c @@ -809,7 +809,7 @@ static int kimage_load_normal_segment(struct kimage *image, if (result < 0) goto out; - ptr = kmap(page); + ptr = kmap_local_page(page); /* Start with a clear page */ clear_page(ptr); ptr += maddr & ~PAGE_MASK; @@ -822,7 +822,7 @@ static int kimage_load_normal_segment(struct kimage *image, memcpy(ptr, kbuf, uchunk); else result = copy_from_user(ptr, buf, uchunk); - kunmap(page); + kunmap_local(ptr); if (result) { result = -EFAULT; goto out; @@ -873,7 +873,7 @@ static int kimage_load_crash_segment(struct kimage *image, goto out; } arch_kexec_post_alloc_pages(page_address(page), 1, 0); - ptr = kmap(page); + ptr = kmap_local_page(page); ptr += maddr & ~PAGE_MASK; mchunk = min_t(size_t, mbytes, PAGE_SIZE - (maddr & ~PAGE_MASK)); @@ -889,7 +889,7 @@ static int kimage_load_crash_segment(struct kimage *image, else result = copy_from_user(ptr, buf, uchunk); kexec_flush_icache_page(page); - kunmap(page); + kunmap_local(ptr); arch_kexec_pre_free_pages(page_address(page), 1); if (result) { result = -EFAULT;