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KVM: arm64: nVHE: Handle hyp panics 

Restore the host context when panicking from hyp to give the best chance
of the panic being clean.

The host requires that registers be preserved such as x18 for the shadow
callstack. If the panic is caused by an exception from EL1, the host
context is still valid so the panic can return straight back to the
host. If the panic comes from EL2 then it's most likely that the hyp
context is active and the host context needs to be restored.

There are windows before and after the host context is saved and
restored that restoration is attempted incorrectly and the panic won't
be clean.

Signed-off-by: Andrew Scull <ascull@google.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20200915104643.2543892-14-ascull@google.com
This commit is contained in:
Andrew Scull 2020-09-15 11:46:37 +01:00 committed by Marc Zyngier
parent 4e3393a969
commit a2e102e20f
3 changed files with 63 additions and 33 deletions
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2
arch/arm64/include/asm/kvm_hyp.h
View File

@ -94,7 +94,7 @@ u64 __guest_enter(struct kvm_vcpu *vcpu);
void __noreturn hyp_panic(void);
#ifdef __KVM_NVHE_HYPERVISOR__
void __noreturn __hyp_do_panic(unsigned long, ...);
void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
#endif
#endif /* __ARM64_KVM_HYP_H__ */

76
arch/arm64/kvm/hyp/nvhe/host.S
View File

@ -47,6 +47,9 @@ SYM_FUNC_START(__host_exit)
ldp x2, x3, [x29, #CPU_XREG_OFFSET(2)]
ldp x4, x5, [x29, #CPU_XREG_OFFSET(4)]
ldp x6, x7, [x29, #CPU_XREG_OFFSET(6)]
/* x0-7 are use for panic arguments */
__host_enter_for_panic:
ldp x8, x9, [x29, #CPU_XREG_OFFSET(8)]
ldp x10, x11, [x29, #CPU_XREG_OFFSET(10)]
ldp x12, x13, [x29, #CPU_XREG_OFFSET(12)]
@ -57,18 +60,38 @@ SYM_FUNC_START(__host_exit)
restore_callee_saved_regs x29
/* Do not touch any register after this! */
__host_enter_without_restoring:
eret
sb
SYM_FUNC_END(__host_exit)
/*
* void __noreturn __hyp_do_panic(bool restore_host, u64 spsr, u64 elr, u64 par);
*/
SYM_FUNC_START(__hyp_do_panic)
/* Load the format arguments into x1-7 */
mov x6, x3
get_vcpu_ptr x7, x3
mrs x3, esr_el2
mrs x4, far_el2
mrs x5, hpfar_el2
/* Prepare and exit to the host's panic funciton. */
mov lr, #(PSR_F_BIT | PSR_I_BIT | PSR_A_BIT | PSR_D_BIT |\
PSR_MODE_EL1h)
msr spsr_el2, lr
ldr lr, =panic
msr elr_el2, lr
eret
sb
/*
* Set the panic format string and enter the host, conditionally
* restoring the host context.
*/
cmp x0, xzr
ldr x0, =__hyp_panic_string
b.eq __host_enter_without_restoring
b __host_enter_for_panic
SYM_FUNC_END(__hyp_do_panic)
.macro host_el1_sync_vect
@ -79,7 +102,7 @@ SYM_FUNC_END(__hyp_do_panic)
lsr x0, x0, #ESR_ELx_EC_SHIFT
cmp x0, #ESR_ELx_EC_HVC64
ldp x0, x1, [sp], #16
b.ne hyp_panic
b.ne __host_exit
/* Check for a stub HVC call */
cmp x0, #HVC_STUB_HCALL_NR
@ -105,16 +128,31 @@ SYM_FUNC_END(__hyp_do_panic)
.endif
.endm
.macro invalid_host_vect
.macro invalid_host_el2_vect
.align 7
/* If a guest is loaded, panic out of it. */
stp x0, x1, [sp, #-16]!
get_loaded_vcpu x0, x1
cbnz x0, __guest_exit_panic
add sp, sp, #16
/*
* The panic may not be clean if the exception is taken before the host
* context has been saved by __host_exit or after the hyp context has
* been partially clobbered by __host_enter.
*/
b hyp_panic
.endm
.macro invalid_host_el1_vect
.align 7
mov x0, xzr /* restore_host = false */
mrs x1, spsr_el2
mrs x2, elr_el2
mrs x3, par_el1
b __hyp_do_panic
.endm
/*
* The host vector does not use an ESB instruction in order to avoid consuming
* SErrors that should only be consumed by the host. Guest entry is deferred by
@ -127,23 +165,23 @@ SYM_FUNC_END(__hyp_do_panic)
*/
.align 11
SYM_CODE_START(__kvm_hyp_host_vector)
invalid_host_vect // Synchronous EL2t
invalid_host_vect // IRQ EL2t
invalid_host_vect // FIQ EL2t
invalid_host_vect // Error EL2t
invalid_host_el2_vect // Synchronous EL2t
invalid_host_el2_vect // IRQ EL2t
invalid_host_el2_vect // FIQ EL2t
invalid_host_el2_vect // Error EL2t
invalid_host_vect // Synchronous EL2h
invalid_host_vect // IRQ EL2h
invalid_host_vect // FIQ EL2h
invalid_host_vect // Error EL2h
invalid_host_el2_vect // Synchronous EL2h
invalid_host_el2_vect // IRQ EL2h
invalid_host_el2_vect // FIQ EL2h
invalid_host_el2_vect // Error EL2h
host_el1_sync_vect // Synchronous 64-bit EL1
invalid_host_vect // IRQ 64-bit EL1
invalid_host_vect // FIQ 64-bit EL1
invalid_host_vect // Error 64-bit EL1
invalid_host_el1_vect // IRQ 64-bit EL1
invalid_host_el1_vect // FIQ 64-bit EL1
invalid_host_el1_vect // Error 64-bit EL1
invalid_host_vect // Synchronous 32-bit EL1
invalid_host_vect // IRQ 32-bit EL1
invalid_host_vect // FIQ 32-bit EL1
invalid_host_vect // Error 32-bit EL1
invalid_host_el1_vect // Synchronous 32-bit EL1
invalid_host_el1_vect // IRQ 32-bit EL1
invalid_host_el1_vect // FIQ 32-bit EL1
invalid_host_el1_vect // Error 32-bit EL1
SYM_CODE_END(__kvm_hyp_host_vector)

18
arch/arm64/kvm/hyp/nvhe/switch.c
View File

@ -242,6 +242,8 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
if (system_uses_irq_prio_masking())
gic_write_pmr(GIC_PRIO_IRQOFF);
host_ctxt->__hyp_running_vcpu = NULL;
return exit_code;
}
@ -250,31 +252,21 @@ void __noreturn hyp_panic(void)
u64 spsr = read_sysreg_el2(SYS_SPSR);
u64 elr = read_sysreg_el2(SYS_ELR);
u64 par = read_sysreg(par_el1);
bool restore_host = true;
struct kvm_cpu_context *host_ctxt;
struct kvm_vcpu *vcpu;
unsigned long str_va;
host_ctxt = &__hyp_this_cpu_ptr(kvm_host_data)->host_ctxt;
vcpu = host_ctxt->__hyp_running_vcpu;
if (read_sysreg(vttbr_el2)) {
if (vcpu) {
__timer_disable_traps(vcpu);
__deactivate_traps(vcpu);
__load_host_stage2();
__sysreg_restore_state_nvhe(host_ctxt);
}
/*
* Force the panic string to be loaded from the literal pool,
* making sure it is a kernel address and not a PC-relative
* reference.
*/
asm volatile("ldr %0, =%1" : "=r" (str_va) : "S" (__hyp_panic_string));
__hyp_do_panic(str_va,
spsr, elr,
read_sysreg(esr_el2), read_sysreg_el2(SYS_FAR),
read_sysreg(hpfar_el2), par, vcpu);
__hyp_do_panic(restore_host, spsr, elr, par);
unreachable();
}