kvm: x86: export TSC information to user-space (4f5758fc) · Commits · 戴 / test

This commit exports the following information to user-space via the newly created per-vcpu debugfs directory: - TSC offset (as a signed number) - TSC scaling ratio - TSC scaling ratio fractinal bits The original intention of this commit was to export only the TSC offset, but the TSC scaling information is exported for completeness. We need to retrieve the TSC offset from user-space in order to support the merging of host and guest traces in trace-cmd. Today, we use the kvm_write_tsc_offset tracepoint, but it has a number of problems (mainly, it requires a running VM to be rebooted, ftrace setup, and also tracepoints are not supposed to be ABIs). The merging of host and guest traces is explained in more detail in this thread: [Qemu-devel] [RFC] host and guest kernel trace merging https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg00887.html This commit creates the following files in debugfs: /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-offset /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio /sys/kernel/debug/kvm/66828-10/vcpu0/tsc-scaling-ratio-frac-bits The last two are only created if TSC scaling is supported. Signed-off-by:

Luiz Capitulino <lcapitulino@redhat.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/debugfs.c

+50 −1

Original line number	Diff line number	Diff line
		@@ -8,13 +8,62 @@
		*
		*/
		#include <linux/kvm_host.h>
		#include <linux/debugfs.h>

		bool kvm_arch_has_vcpu_debugfs(void)
		{
		return false;
		return true;
		}

		static int vcpu_get_tsc_offset(void data, u64 val)
		{
		struct kvm_vcpu vcpu = (struct kvm_vcpu ) data;
		*val = vcpu->arch.tsc_offset;
		return 0;
		}

		DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_offset_fops, vcpu_get_tsc_offset, NULL, "%lld\n");

		static int vcpu_get_tsc_scaling_ratio(void data, u64 val)
		{
		struct kvm_vcpu vcpu = (struct kvm_vcpu ) data;
		*val = vcpu->arch.tsc_scaling_ratio;
		return 0;
		}

		DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_scaling_fops, vcpu_get_tsc_scaling_ratio, NULL, "%llu\n");

		static int vcpu_get_tsc_scaling_frac_bits(void data, u64 val)
		{
		*val = kvm_tsc_scaling_ratio_frac_bits;
		return 0;
		}

		DEFINE_SIMPLE_ATTRIBUTE(vcpu_tsc_scaling_frac_fops, vcpu_get_tsc_scaling_frac_bits, NULL, "%llu\n");

		int kvm_arch_create_vcpu_debugfs(struct kvm_vcpu *vcpu)
		{
		struct dentry *ret;

		ret = debugfs_create_file("tsc-offset", 0444,
		vcpu->debugfs_dentry,
		vcpu, &vcpu_tsc_offset_fops);
		if (!ret)
		return -ENOMEM;

		if (kvm_has_tsc_control) {
		ret = debugfs_create_file("tsc-scaling-ratio", 0444,
		vcpu->debugfs_dentry,
		vcpu, &vcpu_tsc_scaling_fops);
		if (!ret)
		return -ENOMEM;
		ret = debugfs_create_file("tsc-scaling-ratio-frac-bits", 0444,
		vcpu->debugfs_dentry,
		vcpu, &vcpu_tsc_scaling_frac_fops);
		if (!ret)
		return -ENOMEM;

		}

		return 0;
		}

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