kmap_local_page() is the preferred way to create temporary mappings when it is feasible, because the mappings are thread-local and CPU-local. kmap_local_page() uses per-task maps rather than per-CPU maps. This in effect removes the need to preemption in the local CPU while kmap is active, and thus vastly reduces overall system latency. It is also valid to take pagefaults. The use of kmap_atomic() in the SGX code was not an explicit design choice to disable page faults or preemption, and there is no compelling design reason to using kmap_atomic() vs. kmap_local_page(). Link: https://lore.kernel.org/linux-sgx/Y0biN3%2FJsZMa0yUr@xxxxxxxxxx/ For more information on the use of kmap_local_page() vs. kmap_atomic(), please see Documentation/mm/highmem.rst Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx> --- Changes since V1: - Reword commit message to make it more clear why it is preferred to use kmap_local_page() vs. kmap_atomic(). arch/x86/kernel/cpu/sgx/encl.c | 12 ++++++------ arch/x86/kernel/cpu/sgx/ioctl.c | 4 ++-- arch/x86/kernel/cpu/sgx/main.c | 8 ++++---- 3 files changed, 12 insertions(+), 12 deletions(-) diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c index 2c258255a629..68f8b18d2278 100644 --- a/arch/x86/kernel/cpu/sgx/encl.c +++ b/arch/x86/kernel/cpu/sgx/encl.c @@ -160,8 +160,8 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page, return ret; pginfo.addr = encl_page->desc & PAGE_MASK; - pginfo.contents = (unsigned long)kmap_atomic(b.contents); - pcmd_page = kmap_atomic(b.pcmd); + pginfo.contents = (unsigned long)kmap_local_page(b.contents); + pcmd_page = kmap_local_page(b.pcmd); pginfo.metadata = (unsigned long)pcmd_page + b.pcmd_offset; if (secs_page) @@ -187,8 +187,8 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page, */ pcmd_page_empty = !memchr_inv(pcmd_page, 0, PAGE_SIZE); - kunmap_atomic(pcmd_page); - kunmap_atomic((void *)(unsigned long)pginfo.contents); + kunmap_local(pcmd_page); + kunmap_local((void *)(unsigned long)pginfo.contents); get_page(b.pcmd); sgx_encl_put_backing(&b); @@ -197,10 +197,10 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page, if (pcmd_page_empty && !reclaimer_writing_to_pcmd(encl, pcmd_first_page)) { sgx_encl_truncate_backing_page(encl, PFN_DOWN(page_pcmd_off)); - pcmd_page = kmap_atomic(b.pcmd); + pcmd_page = kmap_local_page(b.pcmd); if (memchr_inv(pcmd_page, 0, PAGE_SIZE)) pr_warn("PCMD page not empty after truncate.\n"); - kunmap_atomic(pcmd_page); + kunmap_local(pcmd_page); } put_page(b.pcmd); diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c index ef874828fa6b..03c50f11ad75 100644 --- a/arch/x86/kernel/cpu/sgx/ioctl.c +++ b/arch/x86/kernel/cpu/sgx/ioctl.c @@ -221,11 +221,11 @@ static int __sgx_encl_add_page(struct sgx_encl *encl, pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page); pginfo.addr = encl_page->desc & PAGE_MASK; pginfo.metadata = (unsigned long)secinfo; - pginfo.contents = (unsigned long)kmap_atomic(src_page); + pginfo.contents = (unsigned long)kmap_local_page(src_page); ret = __eadd(&pginfo, sgx_get_epc_virt_addr(epc_page)); - kunmap_atomic((void *)pginfo.contents); + kunmap_local((void *)pginfo.contents); put_page(src_page); return ret ? -EIO : 0; diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c index 0aad028f04d4..e5a37b6e9aa5 100644 --- a/arch/x86/kernel/cpu/sgx/main.c +++ b/arch/x86/kernel/cpu/sgx/main.c @@ -165,17 +165,17 @@ static int __sgx_encl_ewb(struct sgx_epc_page *epc_page, void *va_slot, pginfo.addr = 0; pginfo.secs = 0; - pginfo.contents = (unsigned long)kmap_atomic(backing->contents); - pginfo.metadata = (unsigned long)kmap_atomic(backing->pcmd) + + pginfo.contents = (unsigned long)kmap_local_page(backing->contents); + pginfo.metadata = (unsigned long)kmap_local_page(backing->pcmd) + backing->pcmd_offset; ret = __ewb(&pginfo, sgx_get_epc_virt_addr(epc_page), va_slot); set_page_dirty(backing->pcmd); set_page_dirty(backing->contents); - kunmap_atomic((void *)(unsigned long)(pginfo.metadata - + kunmap_local((void *)(unsigned long)(pginfo.metadata - backing->pcmd_offset)); - kunmap_atomic((void *)(unsigned long)pginfo.contents); + kunmap_local((void *)(unsigned long)pginfo.contents); return ret; } -- 2.38.1
