[PATCH v2 89/94] KVM: arm64: nv: Synchronize PSTATE early on exit
From: Marc Zyngier <maz@kernel.org>
Date: 2020-02-11 18:02:02
Also in:
kvm, kvmarm
Subsystem:
arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest · Maintainers:
Catalin Marinas, Will Deacon, Marc Zyngier, Oliver Upton, Linus Torvalds
The NV code relies on predicates such as is_hyp_ctxt() being
reliable. In turn, is_hyp_ctxt() relies on things like PSTATE
and the virtual HCR_EL2 being accurate.
But with ARMv8.4-NV removing trapping for a large part of the
EL2 system registers (among which HCR_EL2), we can't use such
trapping to synchronize the rest of the state.
Let's look at the following sequence for a VHE guest:
(1) enter guest in host EL0
(2) guest traps to guest vEL2 (no hypervisor intervention)
(3) guest clears virtual HCR_EL2.TGE (no trap either)
(4) host interrupt fires, exit
(5) is_hyp_ctxt() now says "guest" (PSTATE.M==EL1 and TGE==0)
It is obvious that such behaviour would be rather unfortunate,
and lead to interesting, difficult to catch bugs specially if
preemption kicks in (yes, I wasted a whole week chasing this one).
In order to preserve the invariant that a guest entered in host
context must exit in the same context, we must make sure that
is_hyp_ctxt() works correctly. Since we can always observe the
guest value of HCR_EL2.{E2H,TGE} in the VNCR_EL2 page, we solely
need to synchronize PSTATE as early as possible.
This basically amounts to moving from_hw_pstate() as close
as possible to the guest exit point, and fixup_guest_exit()
seems as good a place as any.
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/hyp/switch.c | 51 ++++++++++++++++++++++++++++++++--
arch/arm64/kvm/hyp/sysreg-sr.c | 26 ++---------------
2 files changed, 51 insertions(+), 26 deletions(-)
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 3deea28794e1..c35e67241d8e 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c@@ -537,8 +537,45 @@ static bool __hyp_text handle_tx2_tvm(struct kvm_vcpu *vcpu) * the guest, false when we should restore the host state and return to the * main run loop. */ -static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code) +static bool __hyp_text fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code, + bool hyp_ctxt) { + /* + * Sync pstate back as early as possible, so that is_hyp_ctxt() + * reflects the exact context. It is otherwise possible to get + * confused with a VHE guest and ARMv8.4-NV, such as: + * + * (1) enter guest in host EL0 + * (2) guest traps to guest vEL2 (no hypervisor intervention) + * (3) guest clears virtual HCR_EL2.TGE (no trap either) + * (4) host interrupt fires, exit + * (5) is_hyp_ctxt() now says "guest" (pstate.M==EL1 and TGE==0) + * + * If host preemption occurs, vcpu_load/put() will be very confused. + * This of course only matters to VHE. + */ + + if (has_vhe()) { + u64 pstate = read_sysreg_el2(SYS_SPSR); + + if (unlikely(hyp_ctxt)) { + u64 mode = pstate & PSR_MODE_MASK; + + switch (mode) { + case PSR_MODE_EL1t: + mode = PSR_MODE_EL2t; + break; + case PSR_MODE_EL1h: + mode = PSR_MODE_EL2h; + break; + } + + pstate = (pstate & ~PSR_MODE_MASK) | mode; + } + + *vcpu_cpsr(vcpu) = pstate; + } + if (ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ) vcpu->arch.fault.esr_el2 = read_sysreg_el2(SYS_ESR);
@@ -683,6 +720,7 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu) struct kvm_cpu_context *host_ctxt; struct kvm_cpu_context *guest_ctxt; u64 exit_code; + bool hyp_ctxt; host_ctxt = vcpu->arch.host_cpu_context; host_ctxt->__hyp_running_vcpu = vcpu;
@@ -709,12 +747,19 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu) __set_guest_arch_workaround_state(vcpu); + /* + * Being in HYP context or not is an invariant here. If we enter in + * a given context, we exit in the same context. We can thus only + * sample the context once. + */ + hyp_ctxt = is_hyp_ctxt(vcpu); + do { /* Jump in the fire! */ exit_code = __guest_enter(vcpu, host_ctxt); /* And we're baaack! */ - } while (fixup_guest_exit(vcpu, &exit_code)); + } while (fixup_guest_exit(vcpu, &exit_code, hyp_ctxt)); __set_host_arch_workaround_state(vcpu);
@@ -788,7 +833,7 @@ int __hyp_text __kvm_vcpu_run_nvhe(struct kvm_vcpu *vcpu) exit_code = __guest_enter(vcpu, host_ctxt); /* And we're baaack! */ - } while (fixup_guest_exit(vcpu, &exit_code)); + } while (fixup_guest_exit(vcpu, &exit_code, false)); __set_host_arch_workaround_state(vcpu);
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index eaf78e9b3238..53ece83bf062 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c@@ -109,32 +109,12 @@ static void __hyp_text __sysreg_save_el1_state(struct kvm_cpu_context *ctxt) __sysreg_save_vel1_state(ctxt); } -static u64 __hyp_text from_hw_pstate(const struct kvm_cpu_context *ctxt) -{ - u64 reg = read_sysreg_el2(SYS_SPSR); - - if (__is_hyp_ctxt(ctxt)) { - u64 mode = reg & (PSR_MODE_MASK | PSR_MODE32_BIT); - - switch (mode) { - case PSR_MODE_EL1t: - mode = PSR_MODE_EL2t; - break; - case PSR_MODE_EL1h: - mode = PSR_MODE_EL2h; - break; - } - - return (reg & ~(PSR_MODE_MASK | PSR_MODE32_BIT)) | mode; - } - - return reg; -} - static void __hyp_text __sysreg_save_el2_return_state(struct kvm_cpu_context *ctxt) { + /* On VHE, PSTATE is saved in fixup_guest_exit() */ + if (!has_vhe()) + ctxt->regs.pstate = read_sysreg_el2(SYS_SPSR); ctxt->regs.pc = read_sysreg_el2(SYS_ELR); - ctxt->regs.pstate = from_hw_pstate(ctxt); if (cpus_have_const_cap(ARM64_HAS_RAS_EXTN)) ctxt_sys_reg(ctxt, DISR_EL1) = read_sysreg_s(SYS_VDISR_EL2);
--
2.20.1
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