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Date: Tue, 7 Mar 2017 10:58:38 -0700
From: "Baicar, Tyler" <tbaicar@...eaurora.org>
To: James Morse <james.morse@....com>
Cc: christoffer.dall@...aro.org, marc.zyngier@....com,
pbonzini@...hat.com, rkrcmar@...hat.com, linux@...linux.org.uk,
catalin.marinas@....com, will.deacon@....com, rjw@...ysocki.net,
lenb@...nel.org, matt@...eblueprint.co.uk, robert.moore@...el.com,
lv.zheng@...el.com, nkaje@...eaurora.org, zjzhang@...eaurora.org,
mark.rutland@....com, akpm@...ux-foundation.org,
eun.taik.lee@...sung.com, sandeepa.s.prabhu@...il.com,
labbott@...hat.com, shijie.huang@....com, rruigrok@...eaurora.org,
paul.gortmaker@...driver.com, tn@...ihalf.com, fu.wei@...aro.org,
rostedt@...dmis.org, bristot@...hat.com,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-acpi@...r.kernel.org, linux-efi@...r.kernel.org,
devel@...ica.org, Suzuki.Poulose@....com, punit.agrawal@....com,
astone@...hat.com, harba@...eaurora.org, hanjun.guo@...aro.org,
john.garry@...wei.com, shiju.jose@...wei.com, joe@...ches.com
Subject: Re: [PATCH V12 10/10] arm/arm64: KVM: add guest SEA support
Hello James,
On 3/7/2017 4:48 AM, James Morse wrote:
> On 06/03/17 20:45, Tyler Baicar wrote:
>> Currently external aborts are unsupported by the guest abort
>> handling. Add handling for SEAs so that the host kernel reports
>> SEAs which occur in the guest kernel.
>> diff --git a/arch/arm/include/asm/kvm_arm.h b/arch/arm/include/asm/kvm_arm.h
>> index e22089f..a1a3dff 100644
>> --- a/arch/arm/include/asm/kvm_arm.h
>> +++ b/arch/arm/include/asm/kvm_arm.h
>> @@ -187,6 +187,16 @@
>> #define FSC_FAULT (0x04)
>> #define FSC_ACCESS (0x08)
>> #define FSC_PERM (0x0c)
>> +#define FSC_SEA (0x10)
>> +#define FSC_SEA_TTW0 (0x14)
>> +#define FSC_SEA_TTW1 (0x15)
>> +#define FSC_SEA_TTW2 (0x16)
>> +#define FSC_SEA_TTW3 (0x17)
>> +#define FSC_SECC (0x18)
>> +#define FSC_SECC_TTW0 (0x1c)
> aarch32 doesn't have either of these 'TW0' values, it's an unused encoding.
> (However ...)
>
>> +#define FSC_SECC_TTW1 (0x1d)
>> +#define FSC_SECC_TTW2 (0x1e)
>> +#define FSC_SECC_TTW3 (0x1f)
>>
>> /* Hyp Prefetch Fault Address Register (HPFAR/HDFAR) */
>> #define HPFAR_MASK (~0xf)
>> #endif /* __ASM_ARM_SYSTEM_MISC_H */
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index a5265ed..f3608c9 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -1444,8 +1463,21 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>
>> /* Check the stage-2 fault is trans. fault or write fault */
>> fault_status = kvm_vcpu_trap_get_fault_type(vcpu);
>> - if (fault_status != FSC_FAULT && fault_status != FSC_PERM &&
>> - fault_status != FSC_ACCESS) {
>> +
>> + /* The host kernel will handle the synchronous external abort. There
>> + * is no need to pass the error into the guest.
>> + */
>> + if (is_abort_synchronous(fault_status)) {
>> + if(handle_guest_sea((unsigned long)fault_ipa,
>> + kvm_vcpu_get_hsr(vcpu))) {
>
> ... Looking further up in this function:
>> is_iabt = kvm_vcpu_trap_is_iabt(vcpu);
>> if (unlikely(!is_iabt && kvm_vcpu_dabt_isextabt(vcpu))) {
>> kvm_inject_vabt(vcpu);
>> return 1;
>> }
> ... so external data aborts will have already been 'claimed' by kvm and dealt
> with, and we already have a helper for spotting external aborts. (sorry I didn't
> spot it earlier).
>
> We need to do the handle_guest_sea() before this code.
>
> kvm_inject_vabt() makes an SError interrupt pending for the guest. This makes a
> synchronous error asynchronous as the guest may have SError interrupts masked.
>
> I guess this was the best that could be done at the time of (4055710baca8
> "arm/arm64: KVM: Inject virtual abort when guest exits on external abort"), but
> in the light of this firmware-first handling, I'm not sure its the right thing
> to do.
>
> Is it possible for handle_guest_sea() to return whether it actually found any
> work to do? If there was none I think we should keep this kvm_inject_vabt() as
> it is the existing behaviour.
Yes, I'll move the handle_guest_sea() call above this. My testing didn't
call into that if statement for some reason...it made it to the
handle_guest_sea() call successfully.
If there is no work for the GHES code to do it will return and could
still make the kvm_inject_vabt() call. It will also return and do that
same thing if the error was not fatal in GHES...would that be an issue?
>
>> + kvm_err("Failed to handle guest SEA, FSC: EC=%#x xFSC=%#lx ESR_EL2=%#lx\n",
>> + kvm_vcpu_trap_get_class(vcpu),
>> + (unsigned long)kvm_vcpu_trap_get_fault(vcpu),
>> + (unsigned long)kvm_vcpu_get_hsr(vcpu));
>> + return -EFAULT;
>> + }
>> + } else if (fault_status != FSC_FAULT && fault_status != FSC_PERM &&
>> + fault_status != FSC_ACCESS) {
>> kvm_err("Unsupported FSC: EC=%#x xFSC=%#lx ESR_EL2=%#lx\n",
>> kvm_vcpu_trap_get_class(vcpu),
>> (unsigned long)kvm_vcpu_trap_get_fault(vcpu),
>
>> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
>> index b2d57fc..31c5171 100644
>> --- a/arch/arm64/mm/fault.c
>> +++ b/arch/arm64/mm/fault.c
>> @@ -602,6 +602,24 @@ static const char *fault_name(unsigned int esr)
>> }
>>
>> /*
>> + * Handle Synchronous External Aborts that occur in a guest kernel.
>> + */
>> +int handle_guest_sea(unsigned long addr, unsigned int esr)
>> +{
>> + /*
>> + * synchronize_rcu() will wait for nmi_exit(), so no need to
>> + * rcu_read_lock().
>> + */
> This comment has a life of its own! Given we don't always call ghes_notify_sea()
> when we interrupted un-interruptable code its not always true. I think the
> rcu_read_{,un}lock() should go against the list walk (so it looks like the
> examples), and ditch the comment!
:) Okay I will move the rcu calls into ghes_notify_sea() and remove the
comments.
Thanks,
Tyler
>
>> + if(IS_ENABLED(ACPI_APEI_SEA)) {
>> + rcu_read_lock();
>> + ghes_notify_sea();
>> + rcu_read_unlock();
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +/*
>> * Dispatch a data abort to the relevant handler.
>> */
>> asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
>>
--
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