[PATCH v2 0/3] KVM: selftests: arm64: Make sea_to_user skip cleanly

[Like Xu]

This series hardens the arm64 sea_to_user selftest so that it reports a
clean skip on hosts that cannot actually run it, instead of aborting or
silently passing.

The test drives a real recoverable memory UER through APEI EINJ and
expects the guest to consume the poison and exit to userspace with
KVM_EXIT_ARM_SEA. That relies on host and firmware support that is not
present everywhere, and each unmet dependency is now turned into a skip:

  - EINJ injection is driven directly through debugfs, and an unusable
    EINJ (not built, no firmware support, or not running as root) is
    classified from errno and skipped rather than mishandled.
  - Guest memory is backed by 1GB hugepages; with an empty pool the test
    now skips up front instead of failing an mmap() with -ENOMEM.
  - Some firmware only arms EINJ poison as part of the trigger step that
    notrigger=1 skips, so nothing consumable is left for the guest to
    read. That case is detected and skipped rather than reported as a
    spurious KVM_EXIT_MMIO failure.

Tested on an arm64 host with CONFIG_ACPI_APEI_EINJ: on a platform whose
firmware places no consumable poison under notrigger=1 the test now
skips cleanly, and the earlier -ENOMEM and abort paths are gone.

v1 [1] was a single patch doing only the 1GB hugepage check. Following
Marc's review [2], it is expanded into a series that also fixes the EINJ
handling the test depends on.

Test Results:

  Case 1 (echo 0 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages): 

  # timeout set to 120
  # selftests: kvm: sea_to_user
  # Random seed: 0x6b8b4567
  # 1..0 # SKIP - Requirement not met: get_free_hugepages(backing_page_size) >= VM_MEM_SIZE
  ok 1 selftests: kvm: sea_to_user # SKIP
  # 1 skipped test(s) detected.  Consider enabling relevant config options to improve coverage.
  # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0

  Case 2 (rmmod einj):

  # selftests: kvm: sea_to_user
  # Random seed: 0x6b8b4567
  # # Mapped 0x40000 pages: gva=0x80000000 to gpa=0xff80000000
  # # Before EINJect: data=0xbaadcafe
  # # EINJ_GVA=0x81234bad, einj_gpa=0xff81234bad, einj_hva=0xffff41234bad, einj_hpa=0x42c1234bad
  # 1..0 # SKIP need CONFIG_ACPI_APEI_EINJ and firmware EINJ support
  ok 1 selftests: kvm: sea_to_user # SKIP
  # 1 skipped test(s) detected.  Consider enabling relevant config options to improve coverage.
  # Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0

  Case 3 (modprobe einj):

  # selftests: kvm: sea_to_user
  # Random seed: 0x6b8b4567
  # # Mapped 0x40000 pages: gva=0x80000000 to gpa=0xff80000000
  # # Before EINJect: data=0xbaadcafe
  # # EINJ_GVA=0x81234bad, einj_gpa=0xff81234bad, einj_hva=0xffff41234bad, einj_hpa=0x42c1234bad
  # # 0x10 > /sys/kernel/debug/apei/einj/error_type - done
  # # 0x2 > /sys/kernel/debug/apei/einj/flags - done
  # # 0x42c1234bad > /sys/kernel/debug/apei/einj/param1 - done
  # # 0xffffffffffffffff > /sys/kernel/debug/apei/einj/param2 - done
  # # 0x1 > /sys/kernel/debug/apei/einj/notrigger - done
  # # 0x1 > /sys/kernel/debug/apei/einj/error_inject - done
  # # Memory UER EINJected
  # # SIGBUS (7) received, dumping siginfo...
  # # si_signo=7, si_errno=0, si_code=128, si_addr=(nil)
  # not ok 1 Exit with signal unhandled
  ok 1 selftests: kvm: sea_to_user
  # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

Changes since v1:
  - New patch 1: drive EINJ injection directly through debugfs with
    open()/write() instead of access()+popen(). Classify the open()
    errno so an unprivileged run skips as "requires root" instead of
    falsely reporting missing firmware EINJ, and report a genuine write
    failure instead of the ambiguous "Failed... Success (0)".
  - New patch 3: detect when notrigger=1 leaves no consumable poison and
    skip cleanly, instead of exiting with a confusing KVM_EXIT_MMIO.
  - Patch 2 is the original v1 change, unchanged.

Not yet addressed from [2]: dropping the hard 1GB-hugepage and 4kB
base-page requirements. Suggestions on an acceptable backing scheme are
welcome.

[1] https://lore.kernel.org/kvm/20260817080759.25601-1-likexu@xxxxxxxxxxx/
[2] https://lore.kernel.org/all/86y0le9cvz.wl-maz@xxxxxxxxxx/

Like Xu (3):
  KVM: selftests: arm64: Fix EINJ handling in sea_to_user
  KVM: selftests: arm64: Skip sea_to_user without 1GB hugepages
  KVM: selftests: arm64: Skip sea_to_user when EINJ places no poison

 .../testing/selftests/kvm/arm64/sea_to_user.c | 75 +++++++++++++++----
 .../testing/selftests/kvm/include/test_util.h |  1 +
 tools/testing/selftests/kvm/lib/test_util.c   | 15 ++++
 3 files changed, 77 insertions(+), 14 deletions(-)

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