Re: [PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM

From: kbuild test robot
Date: Thu Aug 23 2018 - 15:04:52 EST


Hi Vlastimil,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tip/auto-latest]
[also build test ERROR on next-20180822]
[cannot apply to v4.18]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url: https://github.com/0day-ci/linux/commits/Vlastimil-Babka/x86-speculation-l1tf-suggest-what-to-do-on-systems-with-too-much-RAM/20180824-013859
config: i386-randconfig-x077-201833 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=i386

All errors (new ones prefixed by >>):

In file included from include/linux/kernel.h:14:0,
from arch/x86/include/asm/percpu.h:45,
from arch/x86/include/asm/current.h:6,
from include/linux/sched.h:12,
from include/linux/utsname.h:6,
from arch/x86/kernel/cpu/bugs.c:12:
arch/x86/kernel/cpu/bugs.c: In function 'l1tf_select_mitigation':
>> arch/x86/kernel/cpu/bugs.c:709:12: error: 'max_pfn' undeclared (first use in this function); did you mean 'pgd_pfn'?
((u64) max_pfn << PAGE_SHIFT) - half_pa);
^
include/linux/printk.h:311:34: note: in definition of macro 'pr_info'
printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
^~~~~~~~~~~
arch/x86/kernel/cpu/bugs.c:709:12: note: each undeclared identifier is reported only once for each function it appears in
((u64) max_pfn << PAGE_SHIFT) - half_pa);
^
include/linux/printk.h:311:34: note: in definition of macro 'pr_info'
printk(KERN_INFO pr_fmt(fmt), ##__VA_ARGS__)
^~~~~~~~~~~

vim +709 arch/x86/kernel/cpu/bugs.c

697
698 /*
699 * This is extremely unlikely to happen because almost all
700 * systems have far more MAX_PA/2 than RAM can be fit into
701 * DIMM slots.
702 */
703 half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT;
704 if (e820__mapped_any(half_pa, ULLONG_MAX - half_pa, E820_TYPE_RAM)) {
705 pr_warn("System has more than MAX_PA/2 memory. L1TF mitigation not effective.\n");
706 pr_info("You may make it effective by booting the kernel with mem=%llu parameter.\n",
707 half_pa);
708 pr_info("However, doing so will make up to %llu bytes of RAM unusable.\n",
> 709 ((u64) max_pfn << PAGE_SHIFT) - half_pa);
710 pr_info("Reading Documentation/admin-guide/l1tf.rst might help you decide.");
711 return;
712 }
713
714 setup_force_cpu_cap(X86_FEATURE_L1TF_PTEINV);
715 }
716

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