linux-kernel - Re: [PATCH v3 6/6] KVM: selftests: test KVM_GUESTDBG

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Date:   Mon, 01 Nov 2021 16:43:22 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org
Cc:     Kieran Bingham <kbingham@...nel.org>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Andrew Jones <drjones@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        "H. Peter Anvin" <hpa@...or.com>, Jessica Yu <jeyu@...nel.org>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Yang Weijiang <weijiang.yang@...el.com>,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Shuah Khan <shuah@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v3 6/6] KVM: selftests: test KVM_GUESTDBG_BLOCKIRQ

Paolo Bonzini <pbonzini@...hat.com> writes:

> On 11/08/21 14:29, Maxim Levitsky wrote:
>> Modify debug_regs test to create a pending interrupt
>> and see that it is blocked when single stepping is done
>> with KVM_GUESTDBG_BLOCKIRQ
>> 
>> Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
>> ---
>>   .../testing/selftests/kvm/x86_64/debug_regs.c | 24 ++++++++++++++++---
>>   1 file changed, 21 insertions(+), 3 deletions(-)
>
> I haven't looked very much at this, but the test fails.
>

Same here,

the test passes on AMD but fails consistently on Intel:

# ./x86_64/debug_regs 
==== Test Assertion Failure ====
  x86_64/debug_regs.c:179: run->exit_reason == KVM_EXIT_DEBUG && run->debug.arch.exception == DB_VECTOR && run->debug.arch.pc == target_rip && run->debug.arch.dr6 == target_dr6
  pid=13434 tid=13434 errno=0 - Success
     1	0x00000000004027c6: main at debug_regs.c:179
     2	0x00007f65344cf554: ?? ??:0
     3	0x000000000040294a: _start at ??:?
  SINGLE_STEP[1]: exit 8 exception 1 rip 0x402a25 (should be 0x402a27) dr6 0xffff4ff0 (should be 0xffff4ff0)

(I know I'm late to the party).

> Paolo
>
>> diff --git a/tools/testing/selftests/kvm/x86_64/debug_regs.c b/tools/testing/selftests/kvm/x86_64/debug_regs.c
>> index 6097a8283377..5f078db1bcba 100644
>> --- a/tools/testing/selftests/kvm/x86_64/debug_regs.c
>> +++ b/tools/testing/selftests/kvm/x86_64/debug_regs.c
>> @@ -8,12 +8,15 @@
>>   #include <string.h>
>>   #include "kvm_util.h"
>>   #include "processor.h"
>> +#include "apic.h"
>>   
>>   #define VCPU_ID 0
>>   
>>   #define DR6_BD		(1 << 13)
>>   #define DR7_GD		(1 << 13)
>>   
>> +#define IRQ_VECTOR 0xAA
>> +
>>   /* For testing data access debug BP */
>>   uint32_t guest_value;
>>   
>> @@ -21,6 +24,11 @@ extern unsigned char sw_bp, hw_bp, write_data, ss_start, bd_start;
>>   
>>   static void guest_code(void)
>>   {
>> +	/* Create a pending interrupt on current vCPU */
>> +	x2apic_enable();
>> +	x2apic_write_reg(APIC_ICR, APIC_DEST_SELF | APIC_INT_ASSERT |
>> +			 APIC_DM_FIXED | IRQ_VECTOR);
>> +
>>   	/*
>>   	 * Software BP tests.
>>   	 *
>> @@ -38,12 +46,19 @@ static void guest_code(void)
>>   		     "mov %%rax,%0;\n\t write_data:"
>>   		     : "=m" (guest_value) : : "rax");
>>   
>> -	/* Single step test, covers 2 basic instructions and 2 emulated */
>> +	/*
>> +	 * Single step test, covers 2 basic instructions and 2 emulated
>> +	 *
>> +	 * Enable interrupts during the single stepping to see that
>> +	 * pending interrupt we raised is not handled due to KVM_GUESTDBG_BLOCKIRQ
>> +	 */
>>   	asm volatile("ss_start: "
>> +		     "sti\n\t"
>>   		     "xor %%eax,%%eax\n\t"
>>   		     "cpuid\n\t"
>>   		     "movl $0x1a0,%%ecx\n\t"
>>   		     "rdmsr\n\t"
>> +		     "cli\n\t"
>>   		     : : : "eax", "ebx", "ecx", "edx");
>>   
>>   	/* DR6.BD test */
>> @@ -72,11 +87,13 @@ int main(void)
>>   	uint64_t cmd;
>>   	int i;
>>   	/* Instruction lengths starting at ss_start */
>> -	int ss_size[4] = {
>> +	int ss_size[6] = {
>> +		1,		/* sti*/
>>   		2,		/* xor */
>>   		2,		/* cpuid */
>>   		5,		/* mov */
>>   		2,		/* rdmsr */
>> +		1,		/* cli */
>>   	};
>>   
>>   	if (!kvm_check_cap(KVM_CAP_SET_GUEST_DEBUG)) {
>> @@ -154,7 +171,8 @@ int main(void)
>>   	for (i = 0; i < (sizeof(ss_size) / sizeof(ss_size[0])); i++) {
>>   		target_rip += ss_size[i];
>>   		CLEAR_DEBUG();
>> -		debug.control = KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_SINGLESTEP;
>> +		debug.control = KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_SINGLESTEP |
>> +				KVM_GUESTDBG_BLOCKIRQ;
>>   		debug.arch.debugreg[7] = 0x00000400;
>>   		APPLY_DEBUG();
>>   		vcpu_run(vm, VCPU_ID);
>> 
>

-- 
Vitaly