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  1. 29 Mar, 2022 1 commit
    • David Matlack's avatar
      KVM: Prevent module exit until all VMs are freed · 5f6de5cb
      David Matlack authored 
      Tie the lifetime the KVM module to the lifetime of each VM via
kvm.users_count. This way anything that grabs a reference to the VM via
kvm_get_kvm() cannot accidentally outlive the KVM module.

Prior to this commit, the lifetime of the KVM module was tied to the
lifetime of /dev/kvm file descriptors, VM file descriptors, and vCPU
file descriptors by their respective file_operations "owner" field.
This approach is insufficient because references grabbed via
kvm_get_kvm() do not prevent closing any of the aforementioned file
descriptors.

This fixes a long standing theoretical bug in KVM that at least affects
async page faults. kvm_setup_async_pf() grabs a reference via
kvm_get_kvm(), and drops it in an asynchronous work callback. Nothing
prevents the VM file descriptor from being closed and the KVM module
from being unloaded before this callback runs.

Fixes: af585b92 ("KVM: Halt vcpu if page it tries to access is swapped out")
Fixes: 3d3aab1b ("KVM: set owner of cpu and vm file operations")
Cc: stable@vger.kernel.org
Suggested-by: default avatarBen Gardon <bgardon@google.com>
[ Based on a patch from Ben implemented for Google's kernel. ]
Signed-off-by: default avatarDavid Matlack <dmatlack@google.com>
Message-Id: <20220303183328.1499189-2-dmatlack@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      5f6de5cb
  3. 21 Mar, 2022 8 commits
  5. 18 Mar, 2022 3 commits
  7. 15 Mar, 2022 2 commits
  9. 14 Mar, 2022 6 commits
  11. 11 Mar, 2022 9 commits
  13. 09 Mar, 2022 4 commits
  15. 08 Mar, 2022 7 commits
    • Suravee Suthikulpanit's avatar
      KVM: SVM: Allow AVIC support on system w/ physical APIC ID > 255 · 4a204f78
      Suravee Suthikulpanit authored 
      Expand KVM's mask for the AVIC host physical ID to the full 12 bits defined
by the architecture.  The number of bits consumed by hardware is model
specific, e.g. early CPUs ignored bits 11:8, but there is no way for KVM
to enumerate the "true" size.  So, KVM must allow using all bits, else it
risks rejecting completely legal x2APIC IDs on newer CPUs.

This means KVM relies on hardware to not assign x2APIC IDs that exceed the
"true" width of the field, but presumably hardware is smart enough to tie
the width to the max x2APIC ID.  KVM also relies on hardware to support at
least 8 bits, as the legacy xAPIC ID is writable by software.  But, those
assumptions are unavoidable due to the lack of any way to enumerate the
"true" width.

Cc: stable@vger.kernel.org
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Suggested-by: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarSean Christopherson <seanjc@google.com>
Fixes: 44a95dae ("KVM: x86: Detect and Initialize AVIC support")
Signed-off-by: default avatarSuravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Message-Id: <20220211000851.185799-1-suravee.suthikulpanit@amd.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      4a204f78
    • Sean Christopherson's avatar
      KVM: selftests: Add test to populate a VM with the max possible guest mem · b58c55d5
      Sean Christopherson authored 
      Add a selftest that enables populating a VM with the maximum amount of
guest memory allowed by the underlying architecture.  Abuse KVM's
memslots by mapping a single host memory region into multiple memslots so
that the selftest doesn't require a system with terabytes of RAM.

Default to 512gb of guest memory, which isn't all that interesting, but
should work on all MMUs and doesn't take an exorbitant amount of memory
or time.  E.g. testing with ~64tb of guest memory takes the better part
of an hour, and requires 200gb of memory for KVM's page tables when using
4kb pages.

To inflicit maximum abuse on KVM' MMU, default to 4kb pages (or whatever
the not-hugepage size is) in the backing store (memfd).  Use memfd for
the host backing store to ensure that hugepages are guaranteed when
requested, and to give the user explicit control of the size of hugepage
being tested.

By default, spin up as many vCPUs as there are available to the selftest,
and distribute the work of dirtying each 4kb chunk of memory across all
vCPUs.  Dirtying guest memory forces KVM to populate its page tables, and
also forces KVM to write back accessed/dirty information to struct page
when the guest memory is freed.

On x86, perform two passes with a MMU context reset between each pass to
coerce KVM into dropping all references to the MMU root, e.g. to emulate
a vCPU dropping the last reference.  Perform both passes and all
rendezvous on all architectures in the hope that arm64 and s390x can gain
similar shenanigans in the future.

Measure and report the duration of each operation, which is helpful not
only to verify the test is working as intended, but also to easily
evaluate the performance differences different page sizes.

Provide command line options to limit the amount of guest memory, set the
size of each slot (i.e. of the host memory region), set the number of
vCPUs, and to enable usage of hugepages.
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220226001546.360188-29-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      b58c55d5
    • Sean Christopherson's avatar
      KVM: selftests: Define cpu_relax() helpers for s390 and x86 · 17ae5ebc
      Sean Christopherson authored 
      Add cpu_relax() for s390 and x86 for use in arch-agnostic tests.  arm64
already defines its own version.
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220226001546.360188-28-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      17ae5ebc
    • Sean Christopherson's avatar
      KVM: selftests: Split out helper to allocate guest mem via memfd · a4187c9b
      Sean Christopherson authored 
      Extract the code for allocating guest memory via memfd out of
vm_userspace_mem_region_add() and into a new helper, kvm_memfd_alloc().
A future selftest to populate a guest with the maximum amount of guest
memory will abuse KVM's memslots to alias guest memory regions to a
single memfd-backed host region, i.e. needs to back a guest with memfd
memory without a 1:1 association between a memslot and a memfd instance.

No functional change intended.
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220226001546.360188-27-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      a4187c9b
    • Sean Christopherson's avatar
      KVM: selftests: Move raw KVM_SET_USER_MEMORY_REGION helper to utils · 3d7d6043
      Sean Christopherson authored 
      Move set_memory_region_test's KVM_SET_USER_MEMORY_REGION helper to KVM's
utils so that it can be used by other tests.  Provide a raw version as
well as an assert-success version to reduce the amount of boilerplate
code need for basic usage.

No functional change intended.
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220226001546.360188-26-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      3d7d6043
    • Sean Christopherson's avatar
      KVM: x86/mmu: WARN on any attempt to atomically update REMOVED SPTE · 396fd74d
      Sean Christopherson authored 
      Disallow calling tdp_mmu_set_spte_atomic() with a REMOVED "old" SPTE.
This solves a conundrum introduced by commit 3255530a ("KVM: x86/mmu:
Automatically update iter->old_spte if cmpxchg fails"); if the helper
doesn't update old_spte in the REMOVED case, then theoretically the
caller could get stuck in an infinite loop as it will fail indefinitely
on the REMOVED SPTE.  E.g. until recently, clear_dirty_gfn_range() didn't
check for a present SPTE and would have spun until getting rescheduled.

In practice, only the page fault path should "create" a new SPTE, all
other paths should only operate on existing, a.k.a. shadow present,
SPTEs.  Now that the page fault path pre-checks for a REMOVED SPTE in all
cases, require all other paths to indirectly pre-check by verifying the
target SPTE is a shadow-present SPTE.

Note, this does not guarantee the actual SPTE isn't REMOVED, nor is that
scenario disallowed.  The invariant is only that the caller mustn't
invoke tdp_mmu_set_spte_atomic() if the SPTE was REMOVED when last
observed by the caller.

Cc: David Matlack <dmatlack@google.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-Id: <20220226001546.360188-25-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      396fd74d
    • Sean Christopherson's avatar
      KVM: x86/mmu: Check for a REMOVED leaf SPTE before making the SPTE · 58298b06
      Sean Christopherson authored 
      Explicitly check for a REMOVED leaf SPTE prior to attempting to map
the final SPTE when handling a TDP MMU fault.  Functionally, this is a
nop as tdp_mmu_set_spte_atomic() will eventually detect the frozen SPTE.
Pre-checking for a REMOVED SPTE is a minor optmization, but the real goal
is to allow tdp_mmu_set_spte_atomic() to have an invariant that the "old"
SPTE is never a REMOVED SPTE.
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarBen Gardon <bgardon@google.com>
Message-Id: <20220226001546.360188-24-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
      58298b06
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