在 2019年10月25日 09:38, d.hatayama@xxxxxxxxxxx 写道:> > >> -----Original Message----- >> From: lijiang [mailto:lijiang@xxxxxxxxxx] >> Sent: Friday, October 25, 2019 10:31 AM >> To: Simon Horman <horms@xxxxxxxxxxxx>; Hatayama, Daisuke/畑山 大輔 >> <d.hatayama@xxxxxxxxxxx> >> Cc: linux-kernel@xxxxxxxxxxxxxxx; jgross@xxxxxxxx; Thomas.Lendacky@xxxxxxx; >> bhe@xxxxxxxxxx; x86@xxxxxxxxxx; kexec@xxxxxxxxxxxxxxxxxxx; >> dhowells@xxxxxxxxxx; mingo@xxxxxxxxxx; bp@xxxxxxxxx; ebiederm@xxxxxxxxxxxx; >> hpa@xxxxxxxxx; tglx@xxxxxxxxxxxxx; dyoung@xxxxxxxxxx; vgoyal@xxxxxxxxxx >> Subject: Re: [PATCH 1/2 v5] x86/kdump: always reserve the low 1MiB when the >> crashkernel option is specified >> >> 在 2019年10月24日 19:33, lijiang 写道: >>> 在 2019年10月24日 18:07, Simon Horman 写道: >>>> Hi Linbo, >>>> >>>> thanks for your patch. >>>> >>>> On Wed, Oct 23, 2019 at 10:19:11PM +0800, Lianbo Jiang wrote: >>>>> Kdump kernel will reuse the first 640k region because the real mode >>>>> trampoline has to work in this area. When the vmcore is dumped, the >>>>> old memory in this area may be accessed, therefore, kernel has to >>>>> copy the contents of the first 640k area to a backup region so that >>>>> kdump kernel can read the old memory from the backup area of the >>>>> first 640k area, which is done in the purgatory(). >>>>> >>>>> But, the current handling of copying the first 640k area runs into >>>>> problems when SME is enabled, kernel does not properly copy these >>>>> old memory to the backup area in the purgatory(), thereby, kdump >>>>> kernel reads out the encrypted contents, because the kdump kernel >>>>> must access the first kernel's memory with the encryption bit set >>>>> when SME is enabled in the first kernel. Please refer to this link: >>>>> >>>>> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204793 >>>>> >>>>> Finally, it causes the following errors, and the crash tool gets >>>>> invalid pointers when parsing the vmcore. >>>>> >>>>> crash> kmem -s|grep -i invalid >>>>> kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid >> freepointer:a6086ac099f0c5a4 >>>>> kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid >> freepointer:a6086ac099f0c5a4 >>>>> crash> >>>>> >>>>> To avoid the above errors, when the crashkernel option is specified, >>>>> lets reserve the remaining low 1MiB memory(after reserving real mode >>>>> memory) so that the allocated memory does not fall into the low 1MiB >>>>> area, which makes us not to copy the first 640k content to a backup >>>>> region in purgatory(). This indicates that it does not need to be >>>>> included in crash dumps or used for anything except the processor >>>>> trampolines that must live in the low 1MiB. >>>>> >>>>> Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx> >>>>> --- >>>>> BTW:I also tried to fix the above problem in purgatory(), but there >>>>> are too many restricts in purgatory() context, for example: i can't >>>>> allocate new memory to create the identity mapping page table for >>>>> SME situation. >>>>> >>>>> Currently, there are two places where the first 640k area is needed, >>>>> the first one is in the find_trampoline_placement(), another one is >>>>> in the reserve_real_mode(), and their content doesn't matter. >>>>> >>>>> In addition, also need to clean all the code related to the backup >>>>> region later. >>>>> >>>>> arch/x86/realmode/init.c | 2 ++ >>>>> include/linux/kexec.h | 2 ++ >>>>> kernel/kexec_core.c | 13 +++++++++++++ >>>>> 3 files changed, 17 insertions(+) >>>>> >>>>> diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c >>>>> index 7dce39c8c034..064cc79a015d 100644 >>>>> --- a/arch/x86/realmode/init.c >>>>> +++ b/arch/x86/realmode/init.c >>>>> @@ -3,6 +3,7 @@ >>>>> #include <linux/slab.h> >>>>> #include <linux/memblock.h> >>>>> #include <linux/mem_encrypt.h> >>>>> +#include <linux/kexec.h> >>>>> >>>>> #include <asm/set_memory.h> >>>>> #include <asm/pgtable.h> >>>>> @@ -34,6 +35,7 @@ void __init reserve_real_mode(void) >>>>> >>>>> memblock_reserve(mem, size); >>>>> set_real_mode_mem(mem); >>>>> + kexec_reserve_low_1MiB(); >>>>> } >>>>> >>>>> static void __init setup_real_mode(void) >>>>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h >>>>> index 1776eb2e43a4..30acf1d738bc 100644 >>>>> --- a/include/linux/kexec.h >>>>> +++ b/include/linux/kexec.h >>>>> @@ -306,6 +306,7 @@ extern void __crash_kexec(struct pt_regs *); >>>>> extern void crash_kexec(struct pt_regs *); >>>>> int kexec_should_crash(struct task_struct *); >>>>> int kexec_crash_loaded(void); >>>>> +void __init kexec_reserve_low_1MiB(void); >>>>> void crash_save_cpu(struct pt_regs *regs, int cpu); >>>>> extern int kimage_crash_copy_vmcoreinfo(struct kimage *image); >>>>> >>>>> @@ -397,6 +398,7 @@ static inline void __crash_kexec(struct pt_regs *regs) >> { } >>>>> static inline void crash_kexec(struct pt_regs *regs) { } >>>>> static inline int kexec_should_crash(struct task_struct *p) { return 0; } >>>>> static inline int kexec_crash_loaded(void) { return 0; } >>>>> +static inline void __init kexec_reserve_low_1MiB(void) { } >>>>> #define kexec_in_progress false >>>>> #endif /* CONFIG_KEXEC_CORE */ >>>>> >>>>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c >>>>> index 15d70a90b50d..5bd89f1fee42 100644 >>>>> --- a/kernel/kexec_core.c >>>>> +++ b/kernel/kexec_core.c >>>>> @@ -37,6 +37,7 @@ >>>>> #include <linux/compiler.h> >>>>> #include <linux/hugetlb.h> >>>>> #include <linux/frame.h> >>>>> +#include <linux/memblock.h> >>>>> >>>>> #include <asm/page.h> >>>>> #include <asm/sections.h> >>>>> @@ -70,6 +71,18 @@ struct resource crashk_low_res = { >>>>> .desc = IORES_DESC_CRASH_KERNEL >>>>> }; >>>>> >>>>> +/* >>>>> + * When the crashkernel option is specified, only use the low >>>>> + * 1MiB for the real mode trampoline. >>>>> + */ >>>>> +void __init kexec_reserve_low_1MiB(void) >>>>> +{ >>>>> + if (strstr(boot_command_line, "crashkernel=")) { >>>> >>>> Could you comment on the issue of using strstr which >>>> was raised by Hatayama-san in response to an earlier revision >>>> of this patch? >>>> >>> >>> Thank you, Simon and Hatayama-san. Lets talk about it here. >>> >>>> strstr() matches for example, >> ANYEXTRACHARACTERScrashkernel=ANYEXTRACHARACTERS. >>>> >>>> Is it enough to use cmdline_find_option_bool()? >>>> >>> >>> The cmdline_find_option_bool() will find a boolean option, but the >> crashkernel option >>> is not a boolean option, maybe it looks odd. So, should we use the >> cmdline_find_option() >>> better? >>> >>> +#include <asm/cmdline.h> >>> >>> void __init kexec_reserve_low_1MiB(void) >>> { >>> - if (strstr(boot_command_line, "crashkernel=")) { >>> + char buffer[4]; >>> + >>> + if (cmdline_find_option(boot_command_line, "crashkernel=", >>> + buffer, sizeof(buffer))) { >> Maybe it is simpler as follow: >> >> + if (cmdline_find_option(boot_command_line, "crashkernel=", >> + NULL, 0)) { >> >> Any thoughts? > > I wrote a test kernel module and it works as expected. > Thank you, Hatayama. This is a very good test case. > static int __init testmod_init(void) > { > char cmdline1[] = "x y crashkernel z"; > char cmdline2[] = "x y crashkernel=128M z"; > > printk("\"1: %d\n", > cmdline_find_option_bool(cmdline1, "crashkernel")); > printk("\"2: %d\n", > cmdline_find_option_bool(cmdline1, "crashkernel=")); > printk("\"3: %d\n", > cmdline_find_option_bool(cmdline2, "crashkernel")); > printk("\"4: %d\n", > cmdline_find_option_bool(cmdline2, "crashkernel=")); > > printk("\"5: %d\n", > cmdline_find_option(cmdline1, "crashkernel", NULL, 0)); > printk("\"6: %d\n", > cmdline_find_option(cmdline1, "crashkernel=", NULL, 0)); > printk("\"7: %d\n", > cmdline_find_option(cmdline2, "crashkernel", NULL, 0)); > printk("\"8: %d\n", > cmdline_find_option(cmdline2, "crashkernel=", NULL, 0)); > > return 0; > } > > # dmesg | tail > [85335.355459] "7: 4 > [85335.356923] "8: -1 > [85349.763849] "1: 5 > [85349.765128] "2: 0 > [85349.766159] "3: 0 > [85349.767145] "4: 0 > [85349.768157] "5: -1 > [85349.769259] "6: -1 > [85349.770423] "7: 4 > [85349.771512] "8: -1 > * Returns the length of the argument (regardless of if it was * truncated to fit in the buffer), or -1 on not found. */ static int __cmdline_find_option(const char *cmdline, int max_cmdline_size, const char *option, char *buffer, int bufsize) According to the above code comment, it should be better like this: + if (cmdline_find_option(boot_command_line, "crashkernel", + NULL, 0) > 0) { After i test, i will post again. Thanks. Lianbo >> >> Thanks >> Lianbo >>> memblock_reserve(0, 1<<20); >>> pr_info("Reserving the low 1MiB of memory for >> crashkernel\n"); >>> } >>> >>> And here, no need to parse the arguments of crashkernel(sometimes, which has >> a >>> complicated syntax), so the size of buffer should be enough. What's your >> opinion? >>> >>> Thanks >>> Lianbo >>> >>>> Thanks in advance! >>>> >>>>> + memblock_reserve(0, 1<<20); >>>>> + pr_info("Reserving the low 1MiB of memory for >> crashkernel\n"); >>>>> + } >>>>> +} >>>>> + >>>>> int kexec_should_crash(struct task_struct *p) >>>>> { >>>>> /* >>>>> -- >>>>> 2.17.1 >>>>> >>>>> >>>>> _______________________________________________ >>>>> kexec mailing list >>>>> kexec@xxxxxxxxxxxxxxxxxxx >>>>> http://lists.infradead.org/mailman/listinfo/kexec >>>>> > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
