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-a1-201833 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.4-2) 4.9.4
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)
        ((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 +/max_pfn +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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