From: David Hildenbrand <david@xxxxxxxxxx> Subject: proc/vmcore: convert oldmem_pfn_is_ram callback to more generic vmcore callbacks Let's support multiple registered callbacks, making sure that registering vmcore callbacks cannot fail. Make the callback return a bool instead of an int, handling how to deal with errors internally. Drop unused HAVE_OLDMEM_PFN_IS_RAM. We soon want to make use of this infrastructure from other drivers: virtio-mem, registering one callback for each virtio-mem device, to prevent reading unplugged virtio-mem memory. Handle it via a generic vmcore_cb structure, prepared for future extensions: for example, once we support virtio-mem on s390x where the vmcore is completely constructed in the second kernel, we want to detect and add plugged virtio-mem memory ranges to the vmcore in order for them to get dumped properly. Handle corner cases that are unexpected and shouldn't happen in sane setups: registering a callback after the vmcore has already been opened (warn only) and unregistering a callback after the vmcore has already been opened (warn and essentially read only zeroes from that point on). Link: https://lkml.kernel.org/r/20211005121430.30136-6-david@xxxxxxxxxx Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Baoquan He <bhe@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Cc: Dave Young <dyoung@xxxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Jason Wang <jasowang@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vivek Goyal <vgoyal@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/aperture_64.c | 13 +++- arch/x86/xen/mmu_hvm.c | 11 ++- fs/proc/vmcore.c | 101 ++++++++++++++++++++++---------- include/linux/crash_dump.h | 26 +++++++- 4 files changed, 112 insertions(+), 39 deletions(-) --- a/arch/x86/kernel/aperture_64.c~proc-vmcore-convert-oldmem_pfn_is_ram-callback-to-more-generic-vmcore-callbacks +++ a/arch/x86/kernel/aperture_64.c @@ -73,12 +73,23 @@ static int gart_mem_pfn_is_ram(unsigned (pfn >= aperture_pfn_start + aperture_page_count)); } +#ifdef CONFIG_PROC_VMCORE +static bool gart_oldmem_pfn_is_ram(struct vmcore_cb *cb, unsigned long pfn) +{ + return !!gart_mem_pfn_is_ram(pfn); +} + +static struct vmcore_cb gart_vmcore_cb = { + .pfn_is_ram = gart_oldmem_pfn_is_ram, +}; +#endif + static void __init exclude_from_core(u64 aper_base, u32 aper_order) { aperture_pfn_start = aper_base >> PAGE_SHIFT; aperture_page_count = (32 * 1024 * 1024) << aper_order >> PAGE_SHIFT; #ifdef CONFIG_PROC_VMCORE - WARN_ON(register_oldmem_pfn_is_ram(&gart_mem_pfn_is_ram)); + register_vmcore_cb(&gart_vmcore_cb); #endif #ifdef CONFIG_PROC_KCORE WARN_ON(register_mem_pfn_is_ram(&gart_mem_pfn_is_ram)); --- a/arch/x86/xen/mmu_hvm.c~proc-vmcore-convert-oldmem_pfn_is_ram-callback-to-more-generic-vmcore-callbacks +++ a/arch/x86/xen/mmu_hvm.c @@ -12,10 +12,10 @@ * The kdump kernel has to check whether a pfn of the crashed kernel * was a ballooned page. vmcore is using this function to decide * whether to access a pfn of the crashed kernel. - * Returns 0 if the pfn is not backed by a RAM page, the caller may + * Returns "false" if the pfn is not backed by a RAM page, the caller may * handle the pfn special in this case. */ -static int xen_oldmem_pfn_is_ram(unsigned long pfn) +static bool xen_vmcore_pfn_is_ram(struct vmcore_cb *cb, unsigned long pfn) { struct xen_hvm_get_mem_type a = { .domid = DOMID_SELF, @@ -24,10 +24,13 @@ static int xen_oldmem_pfn_is_ram(unsigne if (HYPERVISOR_hvm_op(HVMOP_get_mem_type, &a)) { pr_warn_once("Unexpected HVMOP_get_mem_type failure\n"); - return -ENXIO; + return true; } return a.mem_type != HVMMEM_mmio_dm; } +static struct vmcore_cb xen_vmcore_cb = { + .pfn_is_ram = xen_vmcore_pfn_is_ram, +}; #endif static void xen_hvm_exit_mmap(struct mm_struct *mm) @@ -61,6 +64,6 @@ void __init xen_hvm_init_mmu_ops(void) if (is_pagetable_dying_supported()) pv_ops.mmu.exit_mmap = xen_hvm_exit_mmap; #ifdef CONFIG_PROC_VMCORE - WARN_ON(register_oldmem_pfn_is_ram(&xen_oldmem_pfn_is_ram)); + register_vmcore_cb(&xen_vmcore_cb); #endif } --- a/fs/proc/vmcore.c~proc-vmcore-convert-oldmem_pfn_is_ram-callback-to-more-generic-vmcore-callbacks +++ a/fs/proc/vmcore.c @@ -62,46 +62,75 @@ core_param(novmcoredd, vmcoredd_disabled /* Device Dump Size */ static size_t vmcoredd_orig_sz; -/* - * Returns > 0 for RAM pages, 0 for non-RAM pages, < 0 on error - * The called function has to take care of module refcounting. - */ -static int (*oldmem_pfn_is_ram)(unsigned long pfn); - -int register_oldmem_pfn_is_ram(int (*fn)(unsigned long pfn)) -{ - if (oldmem_pfn_is_ram) - return -EBUSY; - oldmem_pfn_is_ram = fn; - return 0; +static DECLARE_RWSEM(vmcore_cb_rwsem); +/* List of registered vmcore callbacks. */ +static LIST_HEAD(vmcore_cb_list); +/* Whether we had a surprise unregistration of a callback. */ +static bool vmcore_cb_unstable; +/* Whether the vmcore has been opened once. */ +static bool vmcore_opened; + +void register_vmcore_cb(struct vmcore_cb *cb) +{ + down_write(&vmcore_cb_rwsem); + INIT_LIST_HEAD(&cb->next); + list_add_tail(&cb->next, &vmcore_cb_list); + /* + * Registering a vmcore callback after the vmcore was opened is + * very unusual (e.g., manual driver loading). + */ + if (vmcore_opened) + pr_warn_once("Unexpected vmcore callback registration\n"); + up_write(&vmcore_cb_rwsem); } -EXPORT_SYMBOL_GPL(register_oldmem_pfn_is_ram); +EXPORT_SYMBOL_GPL(register_vmcore_cb); -void unregister_oldmem_pfn_is_ram(void) +void unregister_vmcore_cb(struct vmcore_cb *cb) { - oldmem_pfn_is_ram = NULL; - wmb(); + down_write(&vmcore_cb_rwsem); + list_del(&cb->next); + /* + * Unregistering a vmcore callback after the vmcore was opened is + * very unusual (e.g., forced driver removal), but we cannot stop + * unregistering. + */ + if (vmcore_opened) { + pr_warn_once("Unexpected vmcore callback unregistration\n"); + vmcore_cb_unstable = true; + } + up_write(&vmcore_cb_rwsem); } -EXPORT_SYMBOL_GPL(unregister_oldmem_pfn_is_ram); +EXPORT_SYMBOL_GPL(unregister_vmcore_cb); static bool pfn_is_ram(unsigned long pfn) { - int (*fn)(unsigned long pfn); - /* pfn is ram unless fn() checks pagetype */ + struct vmcore_cb *cb; bool ret = true; - /* - * Ask hypervisor if the pfn is really ram. - * A ballooned page contains no data and reading from such a page - * will cause high load in the hypervisor. - */ - fn = oldmem_pfn_is_ram; - if (fn) - ret = !!fn(pfn); + lockdep_assert_held_read(&vmcore_cb_rwsem); + if (unlikely(vmcore_cb_unstable)) + return false; + + list_for_each_entry(cb, &vmcore_cb_list, next) { + if (unlikely(!cb->pfn_is_ram)) + continue; + ret = cb->pfn_is_ram(cb, pfn); + if (!ret) + break; + } return ret; } +static int open_vmcore(struct inode *inode, struct file *file) +{ + down_read(&vmcore_cb_rwsem); + vmcore_opened = true; + up_read(&vmcore_cb_rwsem); + + return 0; +} + /* Reads a page from the oldmem device from given offset. */ ssize_t read_from_oldmem(char *buf, size_t count, u64 *ppos, int userbuf, @@ -117,6 +146,7 @@ ssize_t read_from_oldmem(char *buf, size offset = (unsigned long)(*ppos % PAGE_SIZE); pfn = (unsigned long)(*ppos / PAGE_SIZE); + down_read(&vmcore_cb_rwsem); do { if (count > (PAGE_SIZE - offset)) nr_bytes = PAGE_SIZE - offset; @@ -136,8 +166,10 @@ ssize_t read_from_oldmem(char *buf, size tmp = copy_oldmem_page(pfn, buf, nr_bytes, offset, userbuf); - if (tmp < 0) + if (tmp < 0) { + up_read(&vmcore_cb_rwsem); return tmp; + } } *ppos += nr_bytes; count -= nr_bytes; @@ -147,6 +179,7 @@ ssize_t read_from_oldmem(char *buf, size offset = 0; } while (count); + up_read(&vmcore_cb_rwsem); return read; } @@ -537,14 +570,19 @@ static int vmcore_remap_oldmem_pfn(struc unsigned long from, unsigned long pfn, unsigned long size, pgprot_t prot) { + int ret; + /* * Check if oldmem_pfn_is_ram was registered to avoid * looping over all pages without a reason. */ - if (oldmem_pfn_is_ram) - return remap_oldmem_pfn_checked(vma, from, pfn, size, prot); + down_read(&vmcore_cb_rwsem); + if (!list_empty(&vmcore_cb_list) || vmcore_cb_unstable) + ret = remap_oldmem_pfn_checked(vma, from, pfn, size, prot); else - return remap_oldmem_pfn_range(vma, from, pfn, size, prot); + ret = remap_oldmem_pfn_range(vma, from, pfn, size, prot); + up_read(&vmcore_cb_rwsem); + return ret; } static int mmap_vmcore(struct file *file, struct vm_area_struct *vma) @@ -668,6 +706,7 @@ static int mmap_vmcore(struct file *file #endif static const struct proc_ops vmcore_proc_ops = { + .proc_open = open_vmcore, .proc_read = read_vmcore, .proc_lseek = default_llseek, .proc_mmap = mmap_vmcore, --- a/include/linux/crash_dump.h~proc-vmcore-convert-oldmem_pfn_is_ram-callback-to-more-generic-vmcore-callbacks +++ a/include/linux/crash_dump.h @@ -91,9 +91,29 @@ static inline void vmcore_unusable(void) elfcorehdr_addr = ELFCORE_ADDR_ERR; } -#define HAVE_OLDMEM_PFN_IS_RAM 1 -extern int register_oldmem_pfn_is_ram(int (*fn)(unsigned long pfn)); -extern void unregister_oldmem_pfn_is_ram(void); +/** + * struct vmcore_cb - driver callbacks for /proc/vmcore handling + * @pfn_is_ram: check whether a PFN really is RAM and should be accessed when + * reading the vmcore. Will return "true" if it is RAM or if the + * callback cannot tell. If any callback returns "false", it's not + * RAM and the page must not be accessed; zeroes should be + * indicated in the vmcore instead. For example, a ballooned page + * contains no data and reading from such a page will cause high + * load in the hypervisor. + * @next: List head to manage registered callbacks internally; initialized by + * register_vmcore_cb(). + * + * vmcore callbacks allow drivers managing physical memory ranges to + * coordinate with vmcore handling code, for example, to prevent accessing + * physical memory ranges that should not be accessed when reading the vmcore, + * although included in the vmcore header as memory ranges to dump. + */ +struct vmcore_cb { + bool (*pfn_is_ram)(struct vmcore_cb *cb, unsigned long pfn); + struct list_head next; +}; +extern void register_vmcore_cb(struct vmcore_cb *cb); +extern void unregister_vmcore_cb(struct vmcore_cb *cb); #else /* !CONFIG_CRASH_DUMP */ static inline bool is_kdump_kernel(void) { return 0; } _
