[PATCH v2 0/9] KVM: x86: never write to memory from kvm_vcpu_check_block

Paolo Bonzini
2022-08-11T21:06:25Z

It took a few months for me to get back to this, and it is lightly tested
only but I wanted to send it out before disappearing for a long weekend.
The story here is that the following backtrace:

[ 1355.807187] kvm_vcpu_map+0x159/0x190 [kvm]
[ 1355.807628] nested_svm_vmexit+0x4c/0x7f0 [kvm_amd]
[ 1355.808036] ? kvm_vcpu_block+0x54/0xa0 [kvm]
[ 1355.808450] svm_check_nested_events+0x97/0x390 [kvm_amd]
[ 1355.808920] kvm_check_nested_events+0x1c/0x40 [kvm]
[ 1355.809396] kvm_arch_vcpu_runnable+0x4e/0x190 [kvm]
[ 1355.809892] kvm_vcpu_check_block+0x4f/0x100 [kvm]
[ 1355.811259] kvm_vcpu_block+0x6b/0xa0 [kvm]

can occur due to kmap being called in non-sleepable (!TASK_RUNNING) context.
The fix is to extend kvm_x86_ops->nested_ops.hv_timer_pending() to cover
all events not already checked in kvm_arch_vcpu_is_runnable(), and then
get rid of the annoying (and wrong) call to kvm_check_nested_events()
from kvm_vcpu_check_block().

Beware, this is not a complete fix, because kvm_guest_apic_has_interrupt()
might still _read_ memory from non-sleepable context. The fix here is
probably to make kvm_arch_vcpu_is_runnable() return -EAGAIN, and in that
case do a round of kvm_vcpu_check_block() polling in sleepable context.

Nevertheless, it is a good start as it pushes the vmexit into vcpu_block().
The series also does a small cleanup pass on kvm_vcpu_{block,halt}(),
removing KVM_REQ_UNHALT in favor of simply the return value from those
functions. This turned out not to be necessary, but I kept it because
it is cleaner anyway and it touches adjacent code.

Paolo

Paolo Bonzini (8):
KVM: x86: check validity of argument to KVM_SET_MP_STATE
KVM: x86: remove return value of kvm_vcpu_block
KVM: x86: make kvm_vcpu_{block,halt} return whether vCPU is runnable
KVM: mips, x86: do not rely on KVM_REQ_UNHALT
KVM: remove KVM_REQ_UNHALT
KVM: x86: make vendor code check for all nested events
KVM: x86: lapic does not have to process INIT if it is blocked
KVM: x86: never write to memory from kvm_vcpu_check_block

Sean Christopherson (1):
KVM: nVMX: Make an event request when pending an MTF nested VM-Exit

Documentation/virt/kvm/vcpu-requests.rst | 28 +----------
arch/arm64/kvm/arm.c | 1 -
arch/mips/kvm/emulate.c | 7 ++-
arch/powerpc/kvm/book3s_pr.c | 1 -
arch/powerpc/kvm/book3s_pr_papr.c | 1 -
arch/powerpc/kvm/booke.c | 1 -
arch/powerpc/kvm/powerpc.c | 1 -
arch/riscv/kvm/vcpu_insn.c | 1 -
arch/s390/kvm/kvm-s390.c | 2 -
arch/x86/include/asm/kvm_host.h | 3 +-
arch/x86/kvm/i8259.c | 2 +-
arch/x86/kvm/lapic.h | 2 +-
arch/x86/kvm/vmx/nested.c | 9 +++-
arch/x86/kvm/vmx/vmx.c | 6 ++-
arch/x86/kvm/x86.c | 55 ++++++++++++++++------
arch/x86/kvm/x86.h | 5 --
arch/x86/kvm/xen.c | 1 -
include/linux/kvm_host.h | 7 ++-
virt/kvm/kvm_main.c | 59 ++++++++++++------------
19 files changed, 94 insertions(+), 98 deletions(-)

--
2.31.1