Re: [PATCH v3 6/6] KVM: selftests: test KVM_GUESTDBG_BLOCKIRQ

[Maxim Levitsky]

On Mon, 2021-11-01 at 16:43 +0100, Vitaly Kuznetsov wrote:
> Paolo Bonzini <pbonzini@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > >   .../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).

Well that is strange. It passes on my intel laptop. Just tested 
(kvm/queue + qemu master, compiled today) :-(

It fails on iteration 1 (and there is iteration 0) which I think means that we
start with RIP on sti, and get #DB on start of xor instruction first (correctly), 
and then we get #DB again on start of xor instruction again?

Something very strange. My laptop has i7-7600U.

Best regards,
	Maxim Levitsky




> 
> > 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);
> > >