From 4dfe4f40d845cdca655b27bf207959855f3e2d62 Mon Sep 17 00:00:00 2001 From: Junaid Shahid Date: Tue, 19 Oct 2021 18:06:27 -0700 Subject: [PATCH] kvm: x86: mmu: Make NX huge page recovery period configurable Currently, the NX huge page recovery thread wakes up every minute and zaps 1/nx_huge_pages_recovery_ratio of the total number of split NX huge pages at a time. This is intended to ensure that only a relatively small number of pages get zapped at a time. But for very large VMs (or more specifically, VMs with a large number of executable pages), a period of 1 minute could still result in this number being too high (unless the ratio is changed significantly, but that can result in split pages lingering on for too long). This change makes the period configurable instead of fixing it at 1 minute. Users of large VMs can then adjust the period and/or the ratio to reduce the number of pages zapped at one time while still maintaining the same overall duration for cycling through the entire list. By default, KVM derives a period from the ratio such that a page will remain on the list for 1 hour on average. Signed-off-by: Junaid Shahid Message-Id: <20211020010627.305925-1-junaids@google.com> Signed-off-by: Paolo Bonzini --- .../admin-guide/kernel-parameters.txt | 9 +++- arch/x86/kvm/mmu/mmu.c | 41 ++++++++++++++----- 2 files changed, 38 insertions(+), 12 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 91ba391f9b32..f780844c8390 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -2353,7 +2353,14 @@ [KVM] Controls how many 4KiB pages are periodically zapped back to huge pages. 0 disables the recovery, otherwise if the value is N KVM will zap 1/Nth of the 4KiB pages every - minute. The default is 60. + period (see below). The default is 60. + + kvm.nx_huge_pages_recovery_period_ms= + [KVM] Controls the time period at which KVM zaps 4KiB pages + back to huge pages. If the value is a non-zero N, KVM will + zap a portion (see ratio above) of the pages every N msecs. + If the value is 0 (the default), KVM will pick a period based + on the ratio, such that a page is zapped after 1 hour on average. kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. Default is 1 (enabled) diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 0460301d0285..f9f228963088 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -58,6 +58,7 @@ extern bool itlb_multihit_kvm_mitigation; int __read_mostly nx_huge_pages = -1; +static uint __read_mostly nx_huge_pages_recovery_period_ms; #ifdef CONFIG_PREEMPT_RT /* Recovery can cause latency spikes, disable it for PREEMPT_RT. */ static uint __read_mostly nx_huge_pages_recovery_ratio = 0; @@ -66,23 +67,26 @@ static uint __read_mostly nx_huge_pages_recovery_ratio = 60; #endif static int set_nx_huge_pages(const char *val, const struct kernel_param *kp); -static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel_param *kp); +static int set_nx_huge_pages_recovery_param(const char *val, const struct kernel_param *kp); static const struct kernel_param_ops nx_huge_pages_ops = { .set = set_nx_huge_pages, .get = param_get_bool, }; -static const struct kernel_param_ops nx_huge_pages_recovery_ratio_ops = { - .set = set_nx_huge_pages_recovery_ratio, +static const struct kernel_param_ops nx_huge_pages_recovery_param_ops = { + .set = set_nx_huge_pages_recovery_param, .get = param_get_uint, }; module_param_cb(nx_huge_pages, &nx_huge_pages_ops, &nx_huge_pages, 0644); __MODULE_PARM_TYPE(nx_huge_pages, "bool"); -module_param_cb(nx_huge_pages_recovery_ratio, &nx_huge_pages_recovery_ratio_ops, +module_param_cb(nx_huge_pages_recovery_ratio, &nx_huge_pages_recovery_param_ops, &nx_huge_pages_recovery_ratio, 0644); __MODULE_PARM_TYPE(nx_huge_pages_recovery_ratio, "uint"); +module_param_cb(nx_huge_pages_recovery_period_ms, &nx_huge_pages_recovery_param_ops, + &nx_huge_pages_recovery_period_ms, 0644); +__MODULE_PARM_TYPE(nx_huge_pages_recovery_period_ms, "uint"); static bool __read_mostly force_flush_and_sync_on_reuse; module_param_named(flush_on_reuse, force_flush_and_sync_on_reuse, bool, 0644); @@ -6145,18 +6149,24 @@ void kvm_mmu_module_exit(void) mmu_audit_disable(); } -static int set_nx_huge_pages_recovery_ratio(const char *val, const struct kernel_param *kp) +static int set_nx_huge_pages_recovery_param(const char *val, const struct kernel_param *kp) { - unsigned int old_val; + bool was_recovery_enabled, is_recovery_enabled; + uint old_period, new_period; int err; - old_val = nx_huge_pages_recovery_ratio; + was_recovery_enabled = nx_huge_pages_recovery_ratio; + old_period = nx_huge_pages_recovery_period_ms; + err = param_set_uint(val, kp); if (err) return err; - if (READ_ONCE(nx_huge_pages) && - !old_val && nx_huge_pages_recovery_ratio) { + is_recovery_enabled = nx_huge_pages_recovery_ratio; + new_period = nx_huge_pages_recovery_period_ms; + + if (READ_ONCE(nx_huge_pages) && is_recovery_enabled && + (!was_recovery_enabled || old_period > new_period)) { struct kvm *kvm; mutex_lock(&kvm_lock); @@ -6219,8 +6229,17 @@ static void kvm_recover_nx_lpages(struct kvm *kvm) static long get_nx_lpage_recovery_timeout(u64 start_time) { - return READ_ONCE(nx_huge_pages) && READ_ONCE(nx_huge_pages_recovery_ratio) - ? start_time + 60 * HZ - get_jiffies_64() + uint ratio = READ_ONCE(nx_huge_pages_recovery_ratio); + uint period = READ_ONCE(nx_huge_pages_recovery_period_ms); + + if (!period && ratio) { + /* Make sure the period is not less than one second. */ + ratio = min(ratio, 3600u); + period = 60 * 60 * 1000 / ratio; + } + + return READ_ONCE(nx_huge_pages) && ratio + ? start_time + msecs_to_jiffies(period) - get_jiffies_64() : MAX_SCHEDULE_TIMEOUT; }