linux-dev/arch/arm64/kvm/fpsimd.c, branch linus/master

KVM: arm64: Always start with clearing SME flag on load

2022-06-07T13:31:30Z

On each vcpu load, we set the KVM_ARM64_HOST_SME_ENABLED flag if SME is enabled for EL0 on the host. This is used to restore the correct state on vpcu put. However, it appears that nothing ever clears this flag. Once set, it will stick until the vcpu is destroyed, which has the potential to spuriously enable SME for userspace. As it turns out, this is due to the SME code being more or less copied from SVE, and inheriting the same shortcomings. We never saw the issue because nothing uses SME, and the amount of testing is probably still pretty low. Fixes: 861262ab8627 ("KVM: arm64: Handle SME host state when running guests") Signed-off-by: Marc Zyngier Reviwed-by: Mark Brown Link: https://lore.kernel.org/r/20220528113829.1043361-3-maz@kernel.org

KVM: arm64: Always start with clearing SVE flag on load

2022-06-07T13:19:23Z

On each vcpu load, we set the KVM_ARM64_HOST_SVE_ENABLED flag if SVE is enabled for EL0 on the host. This is used to restore the correct state on vpcu put. However, it appears that nothing ever clears this flag. Once set, it will stick until the vcpu is destroyed, which has the potential to spuriously enable SVE for userspace. We probably never saw the issue because no VMM uses SVE, but that's still pretty bad. Unconditionally clearing the flag on vcpu load addresses the issue. Fixes: 8383741ab2e7 ("KVM: arm64: Get rid of host SVE tracking/saving") Signed-off-by: Marc Zyngier Cc: stable@vger.kernel.org Reviewed-by: Mark Brown Link: https://lore.kernel.org/r/20220528113829.1043361-2-maz@kernel.org

arm64/sme: Remove _EL0 from name of SVCR - FIXME sysreg.h

2022-05-16T18:50:20Z

The defines for SVCR call it SVCR_EL0 however the architecture calls the register SVCR with no _EL0 suffix. In preparation for generating the sysreg definitions rename to match the architecture, no functional change. Signed-off-by: Mark Brown Link: https://lore.kernel.org/r/20220510161208.631259-6-broonie@kernel.org Signed-off-by: Catalin Marinas

KVM: arm64: Handle SME host state when running guests

2022-04-22T17:51:23Z

While we don't currently support SME in guests we do currently support it for the host system so we need to take care of SME's impact, including the floating point register state, when running guests. Simiarly to SVE we need to manage the traps in CPACR_RL1, what is new is the handling of streaming mode and ZA. Normally we defer any handling of the floating point register state until the guest first uses it however if the system is in streaming mode FPSIMD and SVE operations may generate SME traps which we would need to distinguish from actual attempts by the guest to use SME. Rather than do this for the time being if we are in streaming mode when entering the guest we force the floating point state to be saved immediately and exit streaming mode, meaning that the guest won't generate SME traps for supported operations. We could handle ZA in the access trap similarly to the FPSIMD/SVE state without the disruption caused by streaming mode but for simplicity handle it the same way as streaming mode for now. This will be revisited when we support SME for guests (hopefully before SME hardware becomes available), for now it will only incur additional cost on systems with SME and even there only if streaming mode or ZA are enabled. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Reviewed-by: Marc Zyngier Link: https://lore.kernel.org/r/20220419112247.711548-27-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement ZA context switching

2022-04-22T17:51:02Z

Allocate space for storing ZA on first access to SME and use that to save and restore ZA state when context switching. We do this by using the vector form of the LDR and STR ZA instructions, these do not require streaming mode and have implementation recommendations that they avoid contention issues in shared SMCU implementations. Since ZA is architecturally guaranteed to be zeroed when enabled we do not need to explicitly zero ZA, either we will be restoring from a saved copy or trapping on first use of SME so we know that ZA must be disabled. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-16-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement streaming SVE context switching

2022-04-22T17:51:00Z

When in streaming mode we need to save and restore the streaming mode SVE register state rather than the regular SVE register state. This uses the streaming mode vector length and omits FFR but is otherwise identical, if TIF_SVE is enabled when we are in streaming mode then streaming mode takes precedence. This does not handle use of streaming SVE state with KVM, ptrace or signals. This will be updated in further patches. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-15-broonie@kernel.org Signed-off-by: Catalin Marinas

arm64/sme: Implement SVCR context switching

2022-04-22T17:50:58Z

In SME the use of both streaming SVE mode and ZA are tracked through PSTATE.SM and PSTATE.ZA, visible through the system register SVCR. In order to context switch the floating point state for SME we need to context switch the contents of this register as part of context switching the floating point state. Since changing the vector length exits streaming SVE mode and disables ZA we also make sure we update SVCR appropriately when setting vector length, and similarly ensure that new threads have streaming SVE mode and ZA disabled. Signed-off-by: Mark Brown Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20220419112247.711548-14-broonie@kernel.org Signed-off-by: Catalin Marinas

KVM: arm64: Add comments for context flush and sync callbacks

2022-02-08T14:42:59Z

Add a little bit of information on where _ctxflush_fp() and _ctxsync_fp() are called to help people unfamiliar with the code get up to speed. Signed-off-by: Mark Brown Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20220124155720.3943374-2-broonie@kernel.org

KVM: arm64: pkvm: Unshare guest structs during teardown

2021-12-16T12:58:57Z

Make use of the newly introduced unshare hypercall during guest teardown to unmap guest-related data structures from the hyp stage-1. Signed-off-by: Quentin Perret Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20211215161232.1480836-15-qperret@google.com

KVM: arm64: Introduce kvm_share_hyp()

2021-12-16T12:58:56Z

The create_hyp_mappings() function can currently be called at any point in time. However, its behaviour in protected mode changes widely depending on when it is being called. Prior to KVM init, it is used to create the temporary page-table used to bring-up the hypervisor, and later on it is transparently turned into a 'share' hypercall when the kernel has lost control over the hypervisor stage-1. In order to prepare the ground for also unsharing pages with the hypervisor during guest teardown, introduce a kvm_share_hyp() function to make it clear in which places a share hypercall should be expected, as we will soon need a matching unshare hypercall in all those places. Signed-off-by: Quentin Perret Signed-off-by: Marc Zyngier Link: https://lore.kernel.org/r/20211215161232.1480836-7-qperret@google.com