From 708da51bbdbf6cdeec5b3b992026e94b7c66c05f Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Tue, 16 Sep 2025 12:52:15 +0200 Subject: [PATCH] x86/hyperv: Fix kdump on Azure CVMs Upstream Status: git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git JIRA: https://issues.redhat.com/browse/RHEL-70228 commit a883d6d0d8066d691680ee6425aadb83ca36130b Author: Vitaly Kuznetsov Date: Thu Aug 28 12:16:18 2025 +0300 x86/hyperv: Fix kdump on Azure CVMs Azure CVM instance types featuring a paravisor hang upon kdump. The investigation shows that makedumpfile causes a hang when it steps on a page which was previously share with the host (HVCALL_MODIFY_SPARSE_GPA_PAGE_HOST_VISIBILITY). The new kernel has no knowledge of these 'special' regions (which are Vmbus connection pages, GPADL buffers, ...). There are several ways to approach the issue: - Convey the knowledge about these regions to the new kernel somehow. - Unshare these regions before accessing in the new kernel (it is unclear if there's a way to query the status for a given GPA range). - Unshare these regions before jumping to the new kernel (which this patch implements). To make the procedure as robust as possible, store PFN ranges of shared regions in a linked list instead of storing GVAs and re-using hv_vtom_set_host_visibility(). This also allows to avoid memory allocation on the kdump/kexec path. Signed-off-by: Vitaly Kuznetsov Reviewed-by: Michael Kelley Reviewed-by: Tianyu Lan Signed-off-by: Wei Liu Signed-off-by: Vitaly Kuznetsov --- arch/x86/hyperv/ivm.c | 211 +++++++++++++++++++++++++++++++++++++++++- 1 file changed, 210 insertions(+), 1 deletion(-) diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c index 10d6ac500ac6..42f79526af34 100644 --- a/arch/x86/hyperv/ivm.c +++ b/arch/x86/hyperv/ivm.c @@ -462,6 +462,195 @@ void hv_ivm_msr_read(u64 msr, u64 *value) hv_ghcb_msr_read(msr, value); } +/* + * Keep track of the PFN regions which were shared with the host. The access + * must be revoked upon kexec/kdump (see hv_ivm_clear_host_access()). + */ +struct hv_enc_pfn_region { + struct list_head list; + u64 pfn; + int count; +}; + +static LIST_HEAD(hv_list_enc); +static DEFINE_RAW_SPINLOCK(hv_list_enc_lock); + +static int hv_list_enc_add(const u64 *pfn_list, int count) +{ + struct hv_enc_pfn_region *ent; + unsigned long flags; + u64 pfn; + int i; + + for (i = 0; i < count; i++) { + pfn = pfn_list[i]; + + raw_spin_lock_irqsave(&hv_list_enc_lock, flags); + /* Check if the PFN already exists in some region first */ + list_for_each_entry(ent, &hv_list_enc, list) { + if ((ent->pfn <= pfn) && (ent->pfn + ent->count - 1 >= pfn)) + /* Nothing to do - pfn is already in the list */ + goto unlock_done; + } + + /* + * Check if the PFN is adjacent to an existing region. Growing + * a region can make it adjacent to another one but merging is + * not (yet) implemented for simplicity. A PFN cannot be added + * to two regions to keep the logic in hv_list_enc_remove() + * correct. + */ + list_for_each_entry(ent, &hv_list_enc, list) { + if (ent->pfn + ent->count == pfn) { + /* Grow existing region up */ + ent->count++; + goto unlock_done; + } else if (pfn + 1 == ent->pfn) { + /* Grow existing region down */ + ent->pfn--; + ent->count++; + goto unlock_done; + } + } + raw_spin_unlock_irqrestore(&hv_list_enc_lock, flags); + + /* No adjacent region found -- create a new one */ + ent = kzalloc(sizeof(struct hv_enc_pfn_region), GFP_KERNEL); + if (!ent) + return -ENOMEM; + + ent->pfn = pfn; + ent->count = 1; + + raw_spin_lock_irqsave(&hv_list_enc_lock, flags); + list_add(&ent->list, &hv_list_enc); + +unlock_done: + raw_spin_unlock_irqrestore(&hv_list_enc_lock, flags); + } + + return 0; +} + +static int hv_list_enc_remove(const u64 *pfn_list, int count) +{ + struct hv_enc_pfn_region *ent, *t; + struct hv_enc_pfn_region new_region; + unsigned long flags; + u64 pfn; + int i; + + for (i = 0; i < count; i++) { + pfn = pfn_list[i]; + + raw_spin_lock_irqsave(&hv_list_enc_lock, flags); + list_for_each_entry_safe(ent, t, &hv_list_enc, list) { + if (pfn == ent->pfn + ent->count - 1) { + /* Removing tail pfn */ + ent->count--; + if (!ent->count) { + list_del(&ent->list); + kfree(ent); + } + goto unlock_done; + } else if (pfn == ent->pfn) { + /* Removing head pfn */ + ent->count--; + ent->pfn++; + if (!ent->count) { + list_del(&ent->list); + kfree(ent); + } + goto unlock_done; + } else if (pfn > ent->pfn && pfn < ent->pfn + ent->count - 1) { + /* + * Removing a pfn in the middle. Cut off the tail + * of the existing region and create a template for + * the new one. + */ + new_region.pfn = pfn + 1; + new_region.count = ent->count - (pfn - ent->pfn + 1); + ent->count = pfn - ent->pfn; + goto unlock_split; + } + + } +unlock_done: + raw_spin_unlock_irqrestore(&hv_list_enc_lock, flags); + continue; + +unlock_split: + raw_spin_unlock_irqrestore(&hv_list_enc_lock, flags); + + ent = kzalloc(sizeof(struct hv_enc_pfn_region), GFP_KERNEL); + if (!ent) + return -ENOMEM; + + ent->pfn = new_region.pfn; + ent->count = new_region.count; + + raw_spin_lock_irqsave(&hv_list_enc_lock, flags); + list_add(&ent->list, &hv_list_enc); + raw_spin_unlock_irqrestore(&hv_list_enc_lock, flags); + } + + return 0; +} + +/* Stop new private<->shared conversions */ +static void hv_vtom_kexec_begin(void) +{ + if (!IS_ENABLED(CONFIG_KEXEC_CORE)) + return; + + /* + * Crash kernel reaches here with interrupts disabled: can't wait for + * conversions to finish. + * + * If race happened, just report and proceed. + */ + if (!set_memory_enc_stop_conversion()) + pr_warn("Failed to stop shared<->private conversions\n"); +} + +static void hv_vtom_kexec_finish(void) +{ + struct hv_gpa_range_for_visibility *input; + struct hv_enc_pfn_region *ent; + unsigned long flags; + u64 hv_status; + int cur, i; + + local_irq_save(flags); + input = *this_cpu_ptr(hyperv_pcpu_input_arg); + + if (unlikely(!input)) + goto out; + + list_for_each_entry(ent, &hv_list_enc, list) { + for (i = 0, cur = 0; i < ent->count; i++) { + input->gpa_page_list[cur] = ent->pfn + i; + cur++; + + if (cur == HV_MAX_MODIFY_GPA_REP_COUNT || i == ent->count - 1) { + input->partition_id = HV_PARTITION_ID_SELF; + input->host_visibility = VMBUS_PAGE_NOT_VISIBLE; + input->reserved0 = 0; + input->reserved1 = 0; + hv_status = hv_do_rep_hypercall( + HVCALL_MODIFY_SPARSE_GPA_PAGE_HOST_VISIBILITY, + cur, 0, input, NULL); + WARN_ON_ONCE(!hv_result_success(hv_status)); + cur = 0; + } + } + + } + +out: + local_irq_restore(flags); +} + /* * hv_mark_gpa_visibility - Set pages visible to host via hvcall. * @@ -475,6 +664,7 @@ static int hv_mark_gpa_visibility(u16 count, const u64 pfn[], struct hv_gpa_range_for_visibility *input; u64 hv_status; unsigned long flags; + int ret; /* no-op if partition isolation is not enabled */ if (!hv_is_isolation_supported()) @@ -486,6 +676,13 @@ static int hv_mark_gpa_visibility(u16 count, const u64 pfn[], return -EINVAL; } + if (visibility == VMBUS_PAGE_NOT_VISIBLE) + ret = hv_list_enc_remove(pfn, count); + else + ret = hv_list_enc_add(pfn, count); + if (ret) + return ret; + local_irq_save(flags); input = *this_cpu_ptr(hyperv_pcpu_input_arg); @@ -506,8 +703,18 @@ static int hv_mark_gpa_visibility(u16 count, const u64 pfn[], if (hv_result_success(hv_status)) return 0; + + if (visibility == VMBUS_PAGE_NOT_VISIBLE) + ret = hv_list_enc_add(pfn, count); else - return -EFAULT; + ret = hv_list_enc_remove(pfn, count); + /* + * There's no good way to recover from -ENOMEM here, the accounting is + * wrong either way. + */ + WARN_ON_ONCE(ret); + + return -EFAULT; } /* @@ -669,6 +876,8 @@ void __init hv_vtom_init(void) x86_platform.guest.enc_tlb_flush_required = hv_vtom_tlb_flush_required; x86_platform.guest.enc_status_change_prepare = hv_vtom_clear_present; x86_platform.guest.enc_status_change_finish = hv_vtom_set_host_visibility; + x86_platform.guest.enc_kexec_begin = hv_vtom_kexec_begin; + x86_platform.guest.enc_kexec_finish = hv_vtom_kexec_finish; /* Set WB as the default cache mode. */ mtrr_overwrite_state(NULL, 0, MTRR_TYPE_WRBACK);