Even though the boot protocol stipulates otherwise, an exception has
been made for the EFI stub, and entering the core kernel with the MMU
enabled is permitted. This allows a substantial amount of cache
maintenance to be elided, wich is significant when fast boot times are
critical (e.g., for booting micro-VMs)
Once the initial ID map has been populated, the MMU is disabled as part
of the logic sequence that puts all system registers into a known state.
Any code that needs to execute within the window where the MMU is off is
cleaned to the PoC explicitly, which includes all of HYP text when
entering at EL2.
However, the current sequence of initializing the EL2 system registers
is not safe: HCR_EL2 is set to its nVHE initial state before SCTLR_EL2
is reprogrammed, and this means that a VHE-to-nVHE switch may occur
while the MMU is enabled. This switch causes some system registers as
well as page table descriptors to be interpreted in a different way,
potentially resulting in spurious exceptions relating to MMU
translation.
So disable the MMU explicitly first when entering in EL2 with the MMU
and caches enabled.
Fixes: 617861703830 ("efi: arm64: enter with MMU and caches enabled")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: <stable@vger.kernel.org> # 6.3.x
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240415075412.2347624-6-ardb+git@google.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
The Falkor erratum that results in the need for an ISB before clearing the M bit in SCTLR_ELx only applies to execution at exception level x, and so the workaround is not needed when disabling the EL1 MMU while running at EL2. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Acked-by: Marc Zyngier <maz@kernel.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Link: https://lore.kernel.org/r/20240415075412.2347624-5-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Commit 3944382fa6f2 introduced checks for the FEAT_E2H0 not being
implemented. However, the check is absolutely wrong and makes a
point it testing a bit that is guaranteed to be zero.
On top of that, the detection happens way too late, after the
init_el2_state has done its job.
This went undetected because the HW this was tested on has E2H being
RAO/WI, and not RES1. However, the bug shows up when run as a nested
guest, where HCR_EL2.E2H is not necessarily set to 1. As a result,
booting the kernel in hVHE mode fails with timer accesses being
cought in a trap loop (which was fun to debug).
Fix the check for ID_AA64MMFR4_EL1.E2H0, and set the HCR_EL2.E2H bit
early so that it can be checked by the rest of the init sequence.
With this, hVHE works again in a NV environment that doesn't have
FEAT_E2H0.
Fixes: 3944382fa6f2 ("arm64: Treat HCR_EL2.E2H as RES1 when ID_AA64MMFR4_EL1.E2H0 is negative")
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20240321115414.3169115-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Pull kvm updates from Paolo Bonzini:
"S390:
- Changes to FPU handling came in via the main s390 pull request
- Only deliver to the guest the SCLP events that userspace has
requested
- More virtual vs physical address fixes (only a cleanup since
virtual and physical address spaces are currently the same)
- Fix selftests undefined behavior
x86:
- Fix a restriction that the guest can't program a PMU event whose
encoding matches an architectural event that isn't included in the
guest CPUID. The enumeration of an architectural event only says
that if a CPU supports an architectural event, then the event can
be programmed *using the architectural encoding*. The enumeration
does NOT say anything about the encoding when the CPU doesn't
report support the event *in general*. It might support it, and it
might support it using the same encoding that made it into the
architectural PMU spec
- Fix a variety of bugs in KVM's emulation of RDPMC (more details on
individual commits) and add a selftest to verify KVM correctly
emulates RDMPC, counter availability, and a variety of other
PMC-related behaviors that depend on guest CPUID and therefore are
easier to validate with selftests than with custom guests (aka
kvm-unit-tests)
- Zero out PMU state on AMD if the virtual PMU is disabled, it does
not cause any bug but it wastes time in various cases where KVM
would check if a PMC event needs to be synthesized
- Optimize triggering of emulated events, with a nice ~10%
performance improvement in VM-Exit microbenchmarks when a vPMU is
exposed to the guest
- Tighten the check for "PMI in guest" to reduce false positives if
an NMI arrives in the host while KVM is handling an IRQ VM-Exit
- Fix a bug where KVM would report stale/bogus exit qualification
information when exiting to userspace with an internal error exit
code
- Add a VMX flag in /proc/cpuinfo to report 5-level EPT support
- Rework TDP MMU root unload, free, and alloc to run with mmu_lock
held for read, e.g. to avoid serializing vCPUs when userspace
deletes a memslot
- Tear down TDP MMU page tables at 4KiB granularity (used to be
1GiB). KVM doesn't support yielding in the middle of processing a
zap, and 1GiB granularity resulted in multi-millisecond lags that
are quite impolite for CONFIG_PREEMPT kernels
- Allocate write-tracking metadata on-demand to avoid the memory
overhead when a kernel is built with i915 virtualization support
but the workloads use neither shadow paging nor i915 virtualization
- Explicitly initialize a variety of on-stack variables in the
emulator that triggered KMSAN false positives
- Fix the debugregs ABI for 32-bit KVM
- Rework the "force immediate exit" code so that vendor code
ultimately decides how and when to force the exit, which allowed
some optimization for both Intel and AMD
- Fix a long-standing bug where kvm_has_noapic_vcpu could be left
elevated if vCPU creation ultimately failed, causing extra
unnecessary work
- Cleanup the logic for checking if the currently loaded vCPU is
in-kernel
- Harden against underflowing the active mmu_notifier invalidation
count, so that "bad" invalidations (usually due to bugs elsehwere
in the kernel) are detected earlier and are less likely to hang the
kernel
x86 Xen emulation:
- Overlay pages can now be cached based on host virtual address,
instead of guest physical addresses. This removes the need to
reconfigure and invalidate the cache if the guest changes the gpa
but the underlying host virtual address remains the same
- When possible, use a single host TSC value when computing the
deadline for Xen timers in order to improve the accuracy of the
timer emulation
- Inject pending upcall events when the vCPU software-enables its
APIC to fix a bug where an upcall can be lost (and to follow Xen's
behavior)
- Fall back to the slow path instead of warning if "fast" IRQ
delivery of Xen events fails, e.g. if the guest has aliased xAPIC
IDs
RISC-V:
- Support exception and interrupt handling in selftests
- New self test for RISC-V architectural timer (Sstc extension)
- New extension support (Ztso, Zacas)
- Support userspace emulation of random number seed CSRs
ARM:
- Infrastructure for building KVM's trap configuration based on the
architectural features (or lack thereof) advertised in the VM's ID
registers
- Support for mapping vfio-pci BARs as Normal-NC (vaguely similar to
x86's WC) at stage-2, improving the performance of interacting with
assigned devices that can tolerate it
- Conversion of KVM's representation of LPIs to an xarray, utilized
to address serialization some of the serialization on the LPI
injection path
- Support for _architectural_ VHE-only systems, advertised through
the absence of FEAT_E2H0 in the CPU's ID register
- Miscellaneous cleanups, fixes, and spelling corrections to KVM and
selftests
LoongArch:
- Set reserved bits as zero in CPUCFG
- Start SW timer only when vcpu is blocking
- Do not restart SW timer when it is expired
- Remove unnecessary CSR register saving during enter guest
- Misc cleanups and fixes as usual
Generic:
- Clean up Kconfig by removing CONFIG_HAVE_KVM, which was basically
always true on all architectures except MIPS (where Kconfig
determines the available depending on CPU capabilities). It is
replaced either by an architecture-dependent symbol for MIPS, and
IS_ENABLED(CONFIG_KVM) everywhere else
- Factor common "select" statements in common code instead of
requiring each architecture to specify it
- Remove thoroughly obsolete APIs from the uapi headers
- Move architecture-dependent stuff to uapi/asm/kvm.h
- Always flush the async page fault workqueue when a work item is
being removed, especially during vCPU destruction, to ensure that
there are no workers running in KVM code when all references to
KVM-the-module are gone, i.e. to prevent a very unlikely
use-after-free if kvm.ko is unloaded
- Grab a reference to the VM's mm_struct in the async #PF worker
itself instead of gifting the worker a reference, so that there's
no need to remember to *conditionally* clean up after the worker
Selftests:
- Reduce boilerplate especially when utilize selftest TAP
infrastructure
- Add basic smoke tests for SEV and SEV-ES, along with a pile of
library support for handling private/encrypted/protected memory
- Fix benign bugs where tests neglect to close() guest_memfd files"
* tag 'for-linus' of git://git.kernel.org/pub/scm/virt/kvm/kvm: (246 commits)
selftests: kvm: remove meaningless assignments in Makefiles
KVM: riscv: selftests: Add Zacas extension to get-reg-list test
RISC-V: KVM: Allow Zacas extension for Guest/VM
KVM: riscv: selftests: Add Ztso extension to get-reg-list test
RISC-V: KVM: Allow Ztso extension for Guest/VM
RISC-V: KVM: Forward SEED CSR access to user space
KVM: riscv: selftests: Add sstc timer test
KVM: riscv: selftests: Change vcpu_has_ext to a common function
KVM: riscv: selftests: Add guest helper to get vcpu id
KVM: riscv: selftests: Add exception handling support
LoongArch: KVM: Remove unnecessary CSR register saving during enter guest
LoongArch: KVM: Do not restart SW timer when it is expired
LoongArch: KVM: Start SW timer only when vcpu is blocking
LoongArch: KVM: Set reserved bits as zero in CPUCFG
KVM: selftests: Explicitly close guest_memfd files in some gmem tests
KVM: x86/xen: fix recursive deadlock in timer injection
KVM: pfncache: simplify locking and make more self-contained
KVM: x86/xen: remove WARN_ON_ONCE() with false positives in evtchn delivery
KVM: x86/xen: inject vCPU upcall vector when local APIC is enabled
KVM: x86/xen: improve accuracy of Xen timers
...
Update the early kernel mapping code to take 52-bit virtual addressing into account based on the LPA2 feature. This is a bit more involved than LVA (which is supported with 64k pages only), given that some page table descriptor bits change meaning in this case. To keep the handling in asm to a minimum, the initial ID map is still created with 48-bit virtual addressing, which implies that the kernel image must be loaded into 48-bit addressable physical memory. This is currently required by the boot protocol, even though we happen to support placement outside of that for LVA/64k based configurations. Enabling LPA2 involves more than setting TCR.T1SZ to a lower value, there is also a DS bit in TCR that needs to be set, and which changes the meaning of bits [9:8] in all page table descriptors. Since we cannot enable DS and every live page table descriptor at the same time, let's pivot through another temporary mapping. This avoids the need to reintroduce manipulations of the page tables with the MMU and caches disabled. To permit the LPA2 feature to be overridden on the kernel command line, which may be necessary to work around silicon errata, or to deal with mismatched features on heterogeneous SoC designs, test for CPU feature overrides first, and only then enable LPA2. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20240214122845.2033971-78-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Currently, we detect CPU support for 52-bit virtual addressing (LVA) extremely early, before creating the kernel page tables or enabling the MMU. We cannot override the feature this early, and so large virtual addressing is always enabled on CPUs that implement support for it if the software support for it was enabled at build time. It also means we rely on non-trivial code in asm to deal with this feature. Given that both the ID map and the TTBR1 mapping of the kernel image are guaranteed to be 48-bit addressable, it is not actually necessary to enable support this early, and instead, we can model it as a CPU feature. That way, we can rely on code patching to get the correct TCR.T1SZ values programmed on secondary boot and resume from suspend. On the primary boot path, we simply enable the MMU with 48-bit virtual addressing initially, and update TCR.T1SZ if LVA is supported from C code, right before creating the kernel mapping. Given that TTBR1 still points to reserved_pg_dir at this point, updating TCR.T1SZ should be safe without the need for explicit TLB maintenance. Since this gets rid of all accesses to the vabits_actual variable from asm code that occurred before TCR.T1SZ had been programmed, we no longer have a need for this variable, and we can replace it with a C expression that produces the correct value directly, based on the value of TCR.T1SZ. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20240214122845.2033971-70-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
The asm code that creates the initial ID map is rather intricate and hard to follow. This is problematic because it makes adding support for things like LPA2 or WXN more difficult than necessary. Also, it is parameterized like the rest of the MM code to run with a configurable number of levels, which is rather pointless, given that all AArch64 CPUs implement support for 48-bit virtual addressing, and that many systems exist with DRAM located outside of the 39-bit addressable range, which is the only smaller VA size that is widely used, and we need additional tricks to make things work in that combination. So let's bite the bullet, and rip out all the asm macros, and fiddly code, and replace it with a C implementation based on the newly added routines for creating the early kernel VA mappings. And while at it, create the initial ID map based on 48-bit virtual addressing as well, regardless of the number of configured levels for the kernel proper. Note that this code may execute with the MMU and caches disabled, and is therefore not permitted to make unaligned accesses. This shouldn't generally happen in any case for the algorithm as implemented, but to be sure, let's pass -mstrict-align to the compiler just in case. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20240214122845.2033971-66-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Even though we support loading kernels anywhere in 48-bit addressable physical memory, we create the ID maps based on the number of levels that we happened to configure for the kernel VA and user VA spaces. The reason for this is that the PGD/PUD/PMD based classification of translation levels, along with the associated folding when the number of levels is less than 5, does not permit creating a page table hierarchy of a set number of levels. This means that, for instance, on 39-bit VA kernels we need to configure an additional level above PGD level on the fly, and 36-bit VA kernels still only support 47-bit virtual addressing with this trick applied. Now that we have a separate helper to populate page table hierarchies that does not define the levels in terms of PUDS/PMDS/etc at all, let's reuse it to create the permanent ID map with a fixed VA size of 48 bits. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20240214122845.2033971-64-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
The asm version of the kernel mapping code works fine for creating a coarse grained identity map, but for mapping the kernel down to its exact boundaries with the right attributes, it is not suitable. This is why we create a preliminary RWX kernel mapping first, and then rebuild it from scratch later on. So let's reimplement this in C, in a way that will make it unnecessary to create the kernel page tables yet another time in paging_init(). Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20240214122845.2033971-63-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Now that we can set BSS variables from the early code running from the ID map, we can set memstart_offset_seed directly from the C code that derives the value instead of passing it back and forth between C and asm code. Signed-off-by: Ard Biesheuvel <ardb@kernel.org> Link: https://lore.kernel.org/r/20240214122845.2033971-60-ardb+git@google.com Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>