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KVM: selftests: Verify single-stepping a fastpath VM-Exit exits to userspace

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In x86's debug_regs test, change the RDMSR(MISC_ENABLES) in the single-step
testcase to a WRMSR(TSC_DEADLINE) in order to verify that KVM honors
KVM_GUESTDBG_SINGLESTEP when handling a fastpath VM-Exit.

Note, the extra coverage is effectively Intel-only, as KVM only handles
TSC_DEADLINE in the fastpath when the timer is emulated via the hypervisor
timer, a.k.a. the VMX preemption timer.

Link: https://lore.kernel.org/r/20240830044448.130449-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson
2024-08-29 21:44:48 -07:00
parent 9d15171f39
commit c32e028057
1 changed files with 7 additions and 4 deletions
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11
tools/testing/selftests/kvm/x86_64/debug_regs.c
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@@ -47,15 +47,18 @@ static void guest_code(void)
/*
* 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
* Enable interrupts during the single stepping to see that pending
* interrupt we raised is not handled due to KVM_GUESTDBG_BLOCKIRQ.
*
* Write MSR_IA32_TSC_DEADLINE to verify that KVM's fastpath handler
* exits to userspace due to single-step being enabled.
*/
asm volatile("ss_start: "
"sti\n\t"
"xor %%eax,%%eax\n\t"
"cpuid\n\t"
"movl $0x1a0,%%ecx\n\t"
"rdmsr\n\t"
"movl $" __stringify(MSR_IA32_TSC_DEADLINE) ", %%ecx\n\t"
"wrmsr\n\t"
"cli\n\t"
: : : "eax", "ebx", "ecx", "edx");