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KVM: arm64: selftests: Disable single-step without relying on ucall()

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Automatically disable single-step when the guest reaches the end of the
verified section instead of using an explicit ucall() to ask userspace to
disable single-step.  An upcoming change to implement a pool-based scheme
for ucall() will add an atomic operation (bit test and set) in the guest
ucall code, and if the compiler generate "old school" atomics, e.g.

  40e57c:       c85f7c20        ldxr    x0, [x1]
  40e580:       aa100011        orr     x17, x0, x16
  40e584:       c80ffc31        stlxr   w15, x17, [x1]
  40e588:       35ffffaf        cbnz    w15, 40e57c <__aarch64_ldset8_sync+0x1c>

the guest will hang as the local exclusive monitor is reset by eret,
i.e. the stlxr will always fail due to the debug exception taken to EL2.

Link: https://lore.kernel.org/all/20221006003409.649993-8-seanjc@google.com
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20221117002350.2178351-3-seanjc@google.com
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Sean Christopherson
2022-11-17 00:23:50 +00:00
parent 1cec8bbc17
commit b3d937722d
1 changed files with 15 additions and 13 deletions
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28
tools/testing/selftests/kvm/aarch64/debug-exceptions.c
View File

@@ -241,7 +241,6 @@ static void guest_svc_handler(struct ex_regs *regs)
enum single_step_op {
SINGLE_STEP_ENABLE = 0,
SINGLE_STEP_DISABLE = 1,
};
static void guest_code_ss(int test_cnt)
@@ -258,7 +257,7 @@ static void guest_code_ss(int test_cnt)
GUEST_SYNC(SINGLE_STEP_ENABLE);
/*
* The userspace will veriry that the pc is as expected during
* The userspace will verify that the pc is as expected during
* single step execution between iter_ss_begin and iter_ss_end.
*/
asm volatile("iter_ss_begin:nop\n");
@@ -268,11 +267,9 @@ static void guest_code_ss(int test_cnt)
bvr = read_sysreg(dbgbvr0_el1);
wvr = read_sysreg(dbgwvr0_el1);
/* Userspace disables Single Step when the end is nigh. */
asm volatile("iter_ss_end:\n");
/* Disable Single Step execution */
GUEST_SYNC(SINGLE_STEP_DISABLE);
GUEST_ASSERT(bvr == w_bvr);
GUEST_ASSERT(wvr == w_wvr);
}
@@ -364,15 +361,12 @@ void test_single_step_from_userspace(int test_cnt)
TEST_ASSERT(cmd == UCALL_SYNC,
"Unexpected ucall cmd 0x%lx", cmd);
if (uc.args[1] == SINGLE_STEP_ENABLE) {
debug.control = KVM_GUESTDBG_ENABLE |
KVM_GUESTDBG_SINGLESTEP;
ss_enable = true;
} else {
debug.control = KVM_GUESTDBG_ENABLE;
ss_enable = false;
}
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;
vcpu_guest_debug_set(vcpu, &debug);
continue;
}
@@ -385,6 +379,14 @@ void test_single_step_from_userspace(int test_cnt)
"Unexpected pc 0x%lx (expected 0x%lx)",
pc, test_pc);
if ((pc + 4) == (uint64_t)&iter_ss_end) {
test_pc = 0;
debug.control = KVM_GUESTDBG_ENABLE;
ss_enable = false;
vcpu_guest_debug_set(vcpu, &debug);
continue;
}
/*
* If the current pc is between iter_ss_bgin and
* iter_ss_end, the pc for the next KVM_EXIT_DEBUG should