90fd09f804
Currently the H_CONFER hcall is implemented in kernel virtual mode, meaning that whenever a guest thread does an H_CONFER, all the threads in that virtual core have to exit the guest. This is bad for performance because it interrupts the other threads even if they are doing useful work. The H_CONFER hcall is called by a guest VCPU when it is spinning on a spinlock and it detects that the spinlock is held by a guest VCPU that is currently not running on a physical CPU. The idea is to give this VCPU's time slice to the holder VCPU so that it can make progress towards releasing the lock. To avoid having the other threads exit the guest unnecessarily, we add a real-mode implementation of H_CONFER that checks whether the other threads are doing anything. If all the other threads are idle (i.e. in H_CEDE) or trying to confer (i.e. in H_CONFER), it returns H_TOO_HARD which causes a guest exit and allows the H_CONFER to be handled in virtual mode. Otherwise it spins for a short time (up to 10 microseconds) to give other threads the chance to observe that this thread is trying to confer. The spin loop also terminates when any thread exits the guest or when all other threads are idle or trying to confer. If the timeout is reached, the H_CONFER returns H_SUCCESS. In this case the guest VCPU will recheck the spinlock word and most likely call H_CONFER again. This also improves the implementation of the H_CONFER virtual mode handler. If the VCPU is part of a virtual core (vcore) which is runnable, there will be a 'runner' VCPU which has taken responsibility for running the vcore. In this case we yield to the runner VCPU rather than the target VCPU. We also introduce a check on the target VCPU's yield count: if it differs from the yield count passed to H_CONFER, the target VCPU has run since H_CONFER was called and may have already released the lock. This check is required by PAPR. Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com> Signed-off-by: Paul Mackerras <paulus@samba.org> Signed-off-by: Alexander Graf <agraf@suse.de>
173 lines
4.6 KiB
C
173 lines
4.6 KiB
C
/*
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* Copyright 2011 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License, version 2, as
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* published by the Free Software Foundation.
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*/
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#include <linux/cpu.h>
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#include <linux/kvm_host.h>
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#include <linux/preempt.h>
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#include <linux/export.h>
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#include <linux/sched.h>
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#include <linux/spinlock.h>
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#include <linux/bootmem.h>
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#include <linux/init.h>
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#include <linux/memblock.h>
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#include <linux/sizes.h>
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#include <linux/cma.h>
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#include <linux/bitops.h>
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#include <asm/cputable.h>
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#include <asm/kvm_ppc.h>
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#include <asm/kvm_book3s.h>
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#define KVM_CMA_CHUNK_ORDER 18
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/*
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* Hash page table alignment on newer cpus(CPU_FTR_ARCH_206)
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* should be power of 2.
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*/
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#define HPT_ALIGN_PAGES ((1 << 18) >> PAGE_SHIFT) /* 256k */
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/*
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* By default we reserve 5% of memory for hash pagetable allocation.
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*/
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static unsigned long kvm_cma_resv_ratio = 5;
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static struct cma *kvm_cma;
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static int __init early_parse_kvm_cma_resv(char *p)
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{
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pr_debug("%s(%s)\n", __func__, p);
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if (!p)
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return -EINVAL;
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return kstrtoul(p, 0, &kvm_cma_resv_ratio);
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}
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early_param("kvm_cma_resv_ratio", early_parse_kvm_cma_resv);
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struct page *kvm_alloc_hpt(unsigned long nr_pages)
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{
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VM_BUG_ON(order_base_2(nr_pages) < KVM_CMA_CHUNK_ORDER - PAGE_SHIFT);
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return cma_alloc(kvm_cma, nr_pages, order_base_2(HPT_ALIGN_PAGES));
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}
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EXPORT_SYMBOL_GPL(kvm_alloc_hpt);
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void kvm_release_hpt(struct page *page, unsigned long nr_pages)
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{
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cma_release(kvm_cma, page, nr_pages);
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}
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EXPORT_SYMBOL_GPL(kvm_release_hpt);
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/**
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* kvm_cma_reserve() - reserve area for kvm hash pagetable
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*
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* This function reserves memory from early allocator. It should be
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* called by arch specific code once the early allocator (memblock or bootmem)
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* has been activated and all other subsystems have already allocated/reserved
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* memory.
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*/
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void __init kvm_cma_reserve(void)
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{
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unsigned long align_size;
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struct memblock_region *reg;
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phys_addr_t selected_size = 0;
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/*
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* We need CMA reservation only when we are in HV mode
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*/
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if (!cpu_has_feature(CPU_FTR_HVMODE))
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return;
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/*
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* We cannot use memblock_phys_mem_size() here, because
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* memblock_analyze() has not been called yet.
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*/
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for_each_memblock(memory, reg)
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selected_size += memblock_region_memory_end_pfn(reg) -
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memblock_region_memory_base_pfn(reg);
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selected_size = (selected_size * kvm_cma_resv_ratio / 100) << PAGE_SHIFT;
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if (selected_size) {
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pr_debug("%s: reserving %ld MiB for global area\n", __func__,
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(unsigned long)selected_size / SZ_1M);
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align_size = HPT_ALIGN_PAGES << PAGE_SHIFT;
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cma_declare_contiguous(0, selected_size, 0, align_size,
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KVM_CMA_CHUNK_ORDER - PAGE_SHIFT, false, &kvm_cma);
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}
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}
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/*
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* Real-mode H_CONFER implementation.
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* We check if we are the only vcpu out of this virtual core
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* still running in the guest and not ceded. If so, we pop up
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* to the virtual-mode implementation; if not, just return to
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* the guest.
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*/
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long int kvmppc_rm_h_confer(struct kvm_vcpu *vcpu, int target,
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unsigned int yield_count)
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{
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struct kvmppc_vcore *vc = vcpu->arch.vcore;
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int threads_running;
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int threads_ceded;
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int threads_conferring;
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u64 stop = get_tb() + 10 * tb_ticks_per_usec;
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int rv = H_SUCCESS; /* => don't yield */
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set_bit(vcpu->arch.ptid, &vc->conferring_threads);
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while ((get_tb() < stop) && (VCORE_EXIT_COUNT(vc) == 0)) {
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threads_running = VCORE_ENTRY_COUNT(vc);
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threads_ceded = hweight32(vc->napping_threads);
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threads_conferring = hweight32(vc->conferring_threads);
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if (threads_ceded + threads_conferring >= threads_running) {
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rv = H_TOO_HARD; /* => do yield */
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break;
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}
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}
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clear_bit(vcpu->arch.ptid, &vc->conferring_threads);
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return rv;
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}
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/*
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* When running HV mode KVM we need to block certain operations while KVM VMs
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* exist in the system. We use a counter of VMs to track this.
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*
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* One of the operations we need to block is onlining of secondaries, so we
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* protect hv_vm_count with get/put_online_cpus().
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*/
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static atomic_t hv_vm_count;
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void kvm_hv_vm_activated(void)
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{
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get_online_cpus();
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atomic_inc(&hv_vm_count);
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put_online_cpus();
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}
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EXPORT_SYMBOL_GPL(kvm_hv_vm_activated);
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void kvm_hv_vm_deactivated(void)
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{
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get_online_cpus();
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atomic_dec(&hv_vm_count);
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put_online_cpus();
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}
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EXPORT_SYMBOL_GPL(kvm_hv_vm_deactivated);
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bool kvm_hv_mode_active(void)
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{
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return atomic_read(&hv_vm_count) != 0;
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}
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extern int hcall_real_table[], hcall_real_table_end[];
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int kvmppc_hcall_impl_hv_realmode(unsigned long cmd)
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{
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cmd /= 4;
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if (cmd < hcall_real_table_end - hcall_real_table &&
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hcall_real_table[cmd])
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return 1;
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return 0;
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}
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EXPORT_SYMBOL_GPL(kvmppc_hcall_impl_hv_realmode);
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