[PATCH] arm64: KVM: set right LR register value for 32 bit guest when inject abort
Marc Zyngier
marc.zyngier at arm.com
Fri Oct 13 08:12:44 PDT 2017
On 13/10/17 15:29, gengdongjiu wrote:
> Hi Marc,
> Thank you very much for your time to review it.
>
>> On 12/10/17 17:44, Dongjiu Geng wrote:
>>> When a exception is trapped to EL2, hardware uses ELR_ELx to hold the
>>> current fault instruction address. If KVM wants to inject a abort to
>>> 32 bit guest, it needs to set the LR register for the guest to emulate
>>> this abort happened in the guest. Because ARM32 architecture is
>>> Multi-pipeline, so the LR value has an offset to
>>
>> What does "Multi-pipeline" mean?
>
> I mean the ARM's single-cycle instruction 3-stage pipeline operation, as shown below:
>
> fetch decode execute
> fetch decode execute
> fetch decode execute
>
> when CPU finish instructions fetch, PC=PC + 4
> when CPU finish instructions decode, PC=PC + 8
> when CPU finish instructions execution, PC=PC+12
Yeah, and that's called pipelined execution. "Multi-pipeline" doesn't
mean anything. Also, that's an artefact of the original ARM1
implementation, and not how modern CPUs work anymore.
>
> that is to say, when happen data abort,
> the PC = fault instruction address + 12, LR_abt = fault instruction address + 8
>
> In order to emulate this abort for KVM, LR_abt needs to add an offset 8 when inject data abort.
>
>>
>>> the fault instruction address.
>>>
>>> The offsets applied to Link value for exceptions as shown below, which
>>> should be added for the ARM32 link register(LR).
>>>
>>> Exception Offset, for PE state of:
>>> A32 T32
>>> Undefined Instruction +4 +2
>>> Prefetch Abort +4 +4
>>> Data Abort +8 +8
>>> IRQ or FIQ +4 +4
>>
>> Please document where this table is coming from.
>
>
> Thanks for pointing out. Will add it.
> It come from: DDI0487A_k_armv8_arm_iss10775, "G1.12.3 Overview of exception entry", Table G1-10 Offsets applied to Link value for exceptions taken to non-EL2 modes
>
>>
>>>
>>> Signed-off-by: Dongjiu Geng <gengdongjiu at huawei.com>
>>> Signed-off-by: Haibin Zhang <zhanghaibin7 at huawei.com>
>>>
>>> ---
>>> For example, to the undefined instruction injection:
>>>
>>> 1. Guest OS call SMC(Secure Monitor Call) instruction in the address
>>> 0xc025405c, then Guest traps to hypervisor
>>>
>>> c0254050: e59d5028 ldr r5, [sp, #40] ; 0x28
>>> c0254054: e3a03001 mov r3, #1
>>> c0254058: e1a01003 mov r1, r3
>>> c025405c: e1600070 smc 0
>>> c0254060: e30a0270 movw r0, #41584 ; 0xa270
>>> c0254064: e34c00bf movt r0, #49343 ; 0xc0bf
>>>
>>> 2. KVM injects undefined abort to guest 3. We will find the fault PC
>>> is 0xc0254058, not 0xc025405c.
>>>
>>> [ 12.348072] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
>>> [ 12.349786] Modules linked in:
>>> [ 12.350563] CPU: 1 PID: 71 Comm: cat Not tainted 4.1.0-dirty #25
>>> [ 12.352061] Hardware name: Generic DT based system
>>> [ 12.353275] task: d9d08000 ti: d9cfe000 task.ti: d9cfe000
>>> [ 12.354637] PC is at proc_dointvec+0x20/0x60
>>> [ 12.355717] LR is at proc_sys_call_handler+0xb0/0xc4
>>> [ 12.356972] pc : [<c0254058>] lr : [<c035699c>] psr: a0060013
>>> [ 12.356972] sp : d9cffe90 ip : c0254038 fp : 00000001
>>> [ 12.359824] r10: d9cfff80 r9 : 00000004 r8 : 00000000
>>> [ 12.361132] r7 : bec21cb0 r6 : d9cffec4 r5 : d9cfff80 r4 : c0e82de0
>>> [ 12.362766] r3 : 00000001 r2 : bec21cb0 r1 : 00000001 r0 : c0e82de0
>>> [ 12.364400] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
>>> [ 12.366183] Control: 10c5383d Table: 59d3406a DAC: 00000015
>>> [ 12.367623] Process cat (pid: 71, stack limit = 0xd9cfe220)
>>>
>>> 4. After correct the LR register, it will have right value
>>>
>>> [ 125.763370] Internal error: Oops - undefined instruction: 0 [#2]
>>> SMP ARM [ 125.767010] Modules linked in:
>>> [ 125.768472] CPU: 1 PID: 74 Comm: cat Tainted: G D 4.1.0-dirty #25
>>> [ 125.771854] Hardware name: Generic DT based system [ 125.774053]
>>> task: db0bb900 ti: d9d10000 task.ti: d9d10000 [ 125.776821] PC is at
>>> proc_dointvec+0x24/0x60 [ 125.778919] LR is at
>>> proc_sys_call_handler+0xb0/0xc4
>>> [ 125.781269] pc : [<c025405c>] lr : [<c035699c>] psr: a0060013
>>> [ 125.781269] sp : d9d11e90 ip : c0254038 fp : 00000001 [
>>> 125.786581] r10: d9d11f80 r9 : 00000004 r8 : 00000000 [ 125.789673]
>>> r7 : be92ccb0 r6 : d9d11ec4 r5 : d9d11f80 r4 : c0e82de0 [
>>> 125.792828] r3 : 00000001 r2 : be92ccb0 r1 : 00000001 r0 : c0e82de0
>>> [ 125.795890] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM
>>> Segment user
>>>
>>> For other exception injection, such as Data/Prefetch abort, also needs
>>> to correct
>>> ---
>>> arch/arm64/kvm/inject_fault.c | 18 ++++++++++++------
>>> 1 file changed, 12 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/inject_fault.c
>>> b/arch/arm64/kvm/inject_fault.c index da6a8cf..da93508 100644
>>> --- a/arch/arm64/kvm/inject_fault.c
>>> +++ b/arch/arm64/kvm/inject_fault.c
>>> @@ -33,12 +33,11 @@
>>> #define LOWER_EL_AArch64_VECTOR 0x400
>>> #define LOWER_EL_AArch32_VECTOR 0x600
>>>
>>> -static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32
>>> vect_offset)
>>> +static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset,
>>> + u32 return_offset)
>>> {
>>> unsigned long cpsr;
>>> unsigned long new_spsr_value = *vcpu_cpsr(vcpu);
>>> - bool is_thumb = (new_spsr_value & COMPAT_PSR_T_BIT);
>>> - u32 return_offset = (is_thumb) ? 4 : 0;
>>> u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
>>>
>>> cpsr = mode | COMPAT_PSR_I_BIT;
>>> @@ -65,7 +64,11 @@ static void prepare_fault32(struct kvm_vcpu *vcpu,
>>> u32 mode, u32 vect_offset)
>>>
>>> static void inject_undef32(struct kvm_vcpu *vcpu) {
>>> - prepare_fault32(vcpu, COMPAT_PSR_MODE_UND, 4);
>>> + unsigned long spsr_value = *vcpu_cpsr(vcpu);
>>> + bool is_thumb = (spsr_value & COMPAT_PSR_T_BIT);
>>> + u32 return_offset = (is_thumb) ? 2 : 4;
>>> +
>>> + prepare_fault32(vcpu, COMPAT_PSR_MODE_UND, 4, return_offset);
>>> }
>>>
>>> /*
>>> @@ -75,21 +78,24 @@ static void inject_undef32(struct kvm_vcpu *vcpu)
>>> static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt,
>>> unsigned long addr)
>>> {
>>> - u32 vect_offset;
>>> + u32 vect_offset, return_offset;
>>> u32 *far, *fsr;
>>> bool is_lpae;
>>>
>>> if (is_pabt) {
>>> vect_offset = 12;
>>> + return_offset = 4;
>>> far = &vcpu_cp15(vcpu, c6_IFAR);
>>> fsr = &vcpu_cp15(vcpu, c5_IFSR);
>>> } else { /* !iabt */
>>> vect_offset = 16;
>>> + return_offset = 8;
>>> far = &vcpu_cp15(vcpu, c6_DFAR);
>>> fsr = &vcpu_cp15(vcpu, c5_DFSR);
>>> }
>>>
>>> - prepare_fault32(vcpu, COMPAT_PSR_MODE_ABT | COMPAT_PSR_A_BIT, vect_offset);
>>> + prepare_fault32(vcpu, COMPAT_PSR_MODE_ABT | COMPAT_PSR_A_BIT,
>>> + vect_offset, return_offset);
>>>
>>> *far = addr;
>>>
>>>
>>
>> So instead of adding this extra parameter and littering the code with random constants, why don't you actually implement the table you've
>> put in the commit log and compute the offset in a single place (which is likely to be prepare_fault32)?
>
> Marc,
> It because multiple abort(Undefined Abort/Prefetch Abort/Data Abort) call the prepare_fault32(), if adding to a single place in prepare_fault32(),prepare_fault32() will
> not know whether the Abort injection is for Prefetch Abort or Data Abort or Undefined Abort, then will be confused for the value of "return_offset"
>
> For example:
> inject_abt32() is used to inject prefetch Abort or Data Abort, it passes same parameters to call prepare_fault32() for the two Abort. If adding and computing the offset in a prepare_fault32(),
> it will be confused to compute the offset, because it does not know whether this function call is for prefetch Abort or Data Abort. [1]
>
> If computing the offset in a single place, do you have better idea for that?
Yes. Realise that vect_offset uniquely identify the type of fault we're
trying to inject:
diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
index da6a8cfa54a0..0416f1857c68 100644
--- a/arch/arm64/kvm/inject_fault.c
+++ b/arch/arm64/kvm/inject_fault.c
@@ -33,12 +33,26 @@
#define LOWER_EL_AArch64_VECTOR 0x400
#define LOWER_EL_AArch32_VECTOR 0x600
+/*
+ * Table taken from ARMv8 ARM DDI0487B-B, table G1-10.
+ */
+static u8 return_offsets[8][2] = {
+ [0] = { 0, 0 }, /* Reset, unused */
+ [1] = { 4, 2 }, /* Undefined */
+ [2] = { 0, 0 }, /* SVC, unused */
+ [3] = { 4, 4 }, /* Prefetch abort */
+ [4] = { 8, 8 }, /* Data abort */
+ [5] = { 0, 0 }, /* HVC, unused */
+ [6] = { 4, 4 }, /* IRQ, unused */
+ [7] = { 4, 4 }, /* FIQ, unused */
+};
+
static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
{
unsigned long cpsr;
unsigned long new_spsr_value = *vcpu_cpsr(vcpu);
bool is_thumb = (new_spsr_value & COMPAT_PSR_T_BIT);
- u32 return_offset = (is_thumb) ? 4 : 0;
+ u32 return_offset = return_offsets[vect_offset >> 2][is_thumb];
u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
cpsr = mode | COMPAT_PSR_I_BIT;
Please also update the 32bit code accordingly, as it looks broken too.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
More information about the linux-arm-kernel
mailing list