linux-kernel - Re: [PATCH V7 1/2] KVM: selftests: Add x86

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Date: Sat, 8 Jun 2024 08:12:36 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: <isaku.yamahata@...el.com>, <pbonzini@...hat.com>,
	<erdemaktas@...gle.com>, <vkuznets@...hat.com>, <seanjc@...gle.com>,
	<vannapurve@...gle.com>, <jmattson@...gle.com>, <mlevitsk@...hat.com>,
	<xiaoyao.li@...el.com>, <chao.gao@...el.com>, <rick.p.edgecombe@...el.com>,
	<yuan.yao@...el.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V7 1/2] KVM: selftests: Add x86_64 guest udelay() utility



On 6/6/24 10:42 AM, Reinette Chatre wrote:
> Create udelay() utility for x86_64 tests to match
> udelay() available to ARM and RISC-V tests.
> 
> Calibrate guest frequency using the KVM_GET_TSC_KHZ ioctl()
> and share it between host and guest with the new
> tsc_khz global variable.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> ---
>   .../selftests/kvm/include/x86_64/processor.h      | 15 +++++++++++++++
>   .../testing/selftests/kvm/lib/x86_64/processor.c  |  8 ++++++++
>   2 files changed, 23 insertions(+)
> 
> diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
> index 8eb57de0b587..f3a5881dd821 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
> @@ -23,6 +23,7 @@
>   
>   extern bool host_cpu_is_intel;
>   extern bool host_cpu_is_amd;
> +extern unsigned long tsc_khz;
>   
>   /* Forced emulation prefix, used to invoke the emulator unconditionally. */
>   #define KVM_FEP "ud2; .byte 'k', 'v', 'm';"
> @@ -815,6 +816,20 @@ static inline void cpu_relax(void)
>   	asm volatile("rep; nop" ::: "memory");
>   }
>   
> +static inline void udelay(unsigned long usec)
> +{
> +	unsigned long cycles = tsc_khz / 1000 * usec;
> +	uint64_t start, now;
> +
> +	start = rdtsc();
> +	for (;;) {
> +		now = rdtsc();
> +		if (now - start >= cycles)
> +			break;
> +		cpu_relax();
> +	}
> +}
> +
>   #define ud2()			\
>   	__asm__ __volatile__(	\
>   		"ud2\n"	\
> diff --git a/tools/testing/selftests/kvm/lib/x86_64/processor.c b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> index c664e446136b..6558fece8a36 100644
> --- a/tools/testing/selftests/kvm/lib/x86_64/processor.c
> +++ b/tools/testing/selftests/kvm/lib/x86_64/processor.c
> @@ -25,6 +25,7 @@ vm_vaddr_t exception_handlers;
>   bool host_cpu_is_amd;
>   bool host_cpu_is_intel;
>   bool is_forced_emulation_enabled;
> +unsigned long tsc_khz;
>   
>   static void regs_dump(FILE *stream, struct kvm_regs *regs, uint8_t indent)
>   {
> @@ -628,6 +629,13 @@ void kvm_arch_vm_post_create(struct kvm_vm *vm)
>   
>   		vm_sev_ioctl(vm, KVM_SEV_INIT2, &init);
>   	}
> +
> +	if (kvm_has_cap(KVM_CAP_GET_TSC_KHZ)) {
> +		tsc_khz = __vm_ioctl(vm, KVM_GET_TSC_KHZ, NULL);
> +		if (tsc_khz < 0)

This incorrect type usage will be fixed in next version that I plan
to send on Monday.

> +			tsc_khz = 0;
> +		sync_global_to_guest(vm, tsc_khz);
> +	}
>   }
>   
>   void vcpu_arch_set_entry_point(struct kvm_vcpu *vcpu, void *guest_code)

Reinette