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KVM: arm64: selftests: Enable single-step without a "full" ucall()

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Add a new ucall hook, GUEST_UCALL_NONE(), to allow tests to make ucalls
without allocating a ucall struct, and use it to enable single-step
in ARM's debug-exceptions test.  Like the disable single-step path, the
enabling path also needs to ensure that no exclusive access sequences are
attempted after enabling single-step, as the exclusive monitor is cleared
on ERET from the debug exception taken to EL2.

The test currently "works" because clear_bit() isn't actually an atomic
operation... yet.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20221119013450.2643007-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-11-19 01:34:44 +00:00 committed by Paolo Bonzini
parent ef40757743
commit ef16b2dff4
2 changed files with 19 additions and 10 deletions
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21
tools/testing/selftests/kvm/aarch64/debug-exceptions.c
View File

@ -239,10 +239,6 @@ static void guest_svc_handler(struct ex_regs *regs)
svc_addr = regs->pc;
}
enum single_step_op {
SINGLE_STEP_ENABLE = 0,
};
static void guest_code_ss(int test_cnt)
{
uint64_t i;
@ -253,8 +249,16 @@ static void guest_code_ss(int test_cnt)
w_bvr = i << 2;
w_wvr = i << 2;
/* Enable Single Step execution */
GUEST_SYNC(SINGLE_STEP_ENABLE);
/*
* Enable Single Step execution. Note! This _must_ be a bare
* ucall as the ucall() path uses atomic operations to manage
* the ucall structures, and the built-in "atomics" are usually
* implemented via exclusive access instructions. The exlusive
* monitor is cleared on ERET, and so taking debug exceptions
* during a LDREX=>STREX sequence will prevent forward progress
* and hang the guest/test.
*/
GUEST_UCALL_NONE();
/*
* The userspace will verify that the pc is as expected during
@ -356,12 +360,9 @@ void test_single_step_from_userspace(int test_cnt)
break;
}
TEST_ASSERT(cmd == UCALL_SYNC,
TEST_ASSERT(cmd == UCALL_NONE,
"Unexpected ucall cmd 0x%lx", cmd);
TEST_ASSERT(uc.args[1] == SINGLE_STEP_ENABLE,
"Unexpected ucall action 0x%lx", uc.args[1]);
debug.control = KVM_GUESTDBG_ENABLE |
KVM_GUESTDBG_SINGLESTEP;
ss_enable = true;

8
tools/testing/selftests/kvm/include/ucall_common.h
View File

@ -35,6 +35,14 @@ void ucall(uint64_t cmd, int nargs, ...);
uint64_t get_ucall(struct kvm_vcpu *vcpu, struct ucall *uc);
void ucall_init(struct kvm_vm *vm, vm_paddr_t mmio_gpa);
/*
* Perform userspace call without any associated data. This bare call avoids
* allocating a ucall struct, which can be useful if the atomic operations in
* the full ucall() are problematic and/or unwanted. Note, this will come out
* as UCALL_NONE on the backend.
*/
#define GUEST_UCALL_NONE() ucall_arch_do_ucall((vm_vaddr_t)NULL)
#define GUEST_SYNC_ARGS(stage, arg1, arg2, arg3, arg4) \
ucall(UCALL_SYNC, 6, "hello", stage, arg1, arg2, arg3, arg4)
#define GUEST_SYNC(stage) ucall(UCALL_SYNC, 2, "hello", stage)