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Date: Fri, 13 Oct 2017 14:29:56 +0000
From: gengdongjiu <gengdongjiu@...wei.com>
To: Marc Zyngier <marc.zyngier@....com>,
"will.deacon@....com" <will.deacon@....com>,
"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
"rkrcmar@...hat.com" <rkrcmar@...hat.com>,
"catalin.marinas@....com" <catalin.marinas@....com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "Zhanghaibin (Euler)" <zhanghaibin7@...wei.com>,
Huangshaoyu <huangshaoyu@...wei.com>
Subject: Re: [PATCH] arm64: KVM: set right LR register value for 32 bit
guest when inject abort
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
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@...wei.com>
> > Signed-off-by: Haibin Zhang <zhanghaibin7@...wei.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?
[1]
static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt,
unsigned long addr)
{
u32 vect_offset;
u32 *far, *fsr;
bool is_lpae;
......
prepare_fault32(vcpu, COMPAT_PSR_MODE_ABT | COMPAT_PSR_A_BIT, vect_offset);
......
}
>
> Thanks,
>
> M.
> --
> Jazz is not dead. It just smells funny...
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