Re: [PATCH V13 10/10] arm/arm64: KVM: add guest SEA support

[Christoffer Dall]

On Tue, Mar 21, 2017 at 04:47:05PM -0600, 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.

The logic in kvm_handle_guest_abort could deserve an explanation here.

Surely the whole logic of how KVM fits into the picture here and how
we're dealing with synchronous errors could be explained here, based on
the long conversations between you and James on many prior iterations on
this patch.

> 
> Signed-off-by: Tyler Baicar <tbaicar@xxxxxxxxxxxxxx>
> ---
>  arch/arm/include/asm/kvm_arm.h       | 10 +++++++++
>  arch/arm/include/asm/system_misc.h   |  5 +++++
>  arch/arm/kvm/mmu.c                   | 41 ++++++++++++++++++++++++++++++------
>  arch/arm64/include/asm/kvm_arm.h     | 10 +++++++++
>  arch/arm64/include/asm/system_misc.h |  2 ++
>  arch/arm64/mm/fault.c                | 19 +++++++++++++++--
>  drivers/acpi/apei/ghes.c             | 13 ++++++------
>  include/acpi/ghes.h                  |  2 +-
>  8 files changed, 86 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_arm.h b/arch/arm/include/asm/kvm_arm.h
> index a3f0b3d..ebf020b 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)
> +#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)
> diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h
> index a3d61ad..ea45d94 100644
> --- a/arch/arm/include/asm/system_misc.h
> +++ b/arch/arm/include/asm/system_misc.h
> @@ -24,4 +24,9 @@
>  
>  #endif /* !__ASSEMBLY__ */
>  
> +static inline int handle_guest_sea(unsigned long addr, unsigned int esr)
> +{
> +	return -1;
> +}
> +
>  #endif /* __ASM_ARM_SYSTEM_MISC_H */
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 962616f..105b6ab 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -29,6 +29,7 @@
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_emulate.h>
>  #include <asm/virt.h>
> +#include <asm/system_misc.h>
>  
>  #include "trace.h"
>  
> @@ -1406,6 +1407,24 @@ static void handle_access_fault(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa)
>  		kvm_set_pfn_accessed(pfn);
>  }
>  
> +static bool is_abort_synchronous(unsigned long fault_status) {

this naming feels a bit weird to me.  For example, this will return
false for a normal translation fault, which is indeed synchronous.

Below you cann handle_guest_sea conditionally based on the result of
this function, so could it be called is_abort_sea ?

> +	switch (fault_status) {
> +	case FSC_SEA:
> +	case FSC_SEA_TTW0:
> +	case FSC_SEA_TTW1:
> +	case FSC_SEA_TTW2:
> +	case FSC_SEA_TTW3:
> +	case FSC_SECC:
> +	case FSC_SECC_TTW0:
> +	case FSC_SECC_TTW1:
> +	case FSC_SECC_TTW2:
> +	case FSC_SECC_TTW3:
> +		return true;
> +	default:
> +		return false;
> +	}
> +}
> +
>  /**
>   * kvm_handle_guest_abort - handles all 2nd stage aborts
>   * @vcpu:	the VCPU pointer
> @@ -1426,23 +1445,31 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>  	unsigned long hva;
>  	bool is_iabt, write_fault, writable;
>  	gfn_t gfn;
> -	int ret, idx;
> +	int ret, idx, sea_status = 1;
> +
> +	/* Check the stage-2 fault is trans. fault or write fault */

I think this comment was supposed to belong with the check for the three
types below, not for calling kvm_vcpu_trap_get_fault_type, and I also
think the comment is outdated, because it doesn't mention the access
flag.

I suggest either removing the comment, or keep it where it was and
change to say "trans. fault, write fault, acces flag fault, or
sea_status", with some insight into what sea_status means here.

> +	fault_status = kvm_vcpu_trap_get_fault_type(vcpu);
> +
> +	fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
> +
> +	/* The host kernel will handle the synchronous external abort. There
> +	 * is no need to pass the error into the guest.
> +	 */

nit: commenting style.

> +	if (is_abort_synchronous(fault_status))
> +		sea_status = handle_guest_sea((unsigned long)fault_ipa,

will this ever be used on AArch32 in the future?

If so, casting a phys_addr_t for an IPA to an unsigned long is an
incredibly bad idea.  Why not just use phys_addr_t for handle_guest_sea?

> +				    kvm_vcpu_get_hsr(vcpu));
>  
>  	is_iabt = kvm_vcpu_trap_is_iabt(vcpu);
> -	if (unlikely(!is_iabt && kvm_vcpu_dabt_isextabt(vcpu))) {
> +	if (unlikely(!is_iabt && kvm_vcpu_dabt_isextabt(vcpu)) && sea_status) {
>  		kvm_inject_vabt(vcpu);
>  		return 1;
>  	}
>  
> -	fault_ipa = kvm_vcpu_get_fault_ipa(vcpu);
> -
>  	trace_kvm_guest_fault(*vcpu_pc(vcpu), kvm_vcpu_get_hsr(vcpu),
>  			      kvm_vcpu_get_hfar(vcpu), fault_ipa);
>  
> -	/* 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) {
> +	    fault_status != FSC_ACCESS && sea_status) {

I don't understand the maning of sea_status here.  If sea_status is
non-zero then the fault_status matters, but if sea_status is zero, then
we just continue by handling this as an MMIO abort or a user fault?

What am I missing here?



>  		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/include/asm/kvm_arm.h b/arch/arm64/include/asm/kvm_arm.h
> index 6e99978..61d694c 100644
> --- a/arch/arm64/include/asm/kvm_arm.h
> +++ b/arch/arm64/include/asm/kvm_arm.h
> @@ -204,6 +204,16 @@
>  #define FSC_FAULT	ESR_ELx_FSC_FAULT
>  #define FSC_ACCESS	ESR_ELx_FSC_ACCESS
>  #define FSC_PERM	ESR_ELx_FSC_PERM
> +#define FSC_SEA		ESR_ELx_FSC_EXTABT
> +#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)
> +#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	(~UL(0xf))
> diff --git a/arch/arm64/include/asm/system_misc.h b/arch/arm64/include/asm/system_misc.h
> index bc81243..5b2cecd 100644
> --- a/arch/arm64/include/asm/system_misc.h
> +++ b/arch/arm64/include/asm/system_misc.h
> @@ -58,4 +58,6 @@ void hook_debug_fault_code(int nr, int (*fn)(unsigned long, unsigned int,
>  
>  #endif	/* __ASSEMBLY__ */
>  
> +int handle_guest_sea(unsigned long addr, unsigned int esr);
> +
>  #endif	/* __ASM_SYSTEM_MISC_H */
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index f7372ce..ee96307 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -497,6 +497,7 @@ static int do_bad(unsigned long addr, unsigned int esr, struct pt_regs *regs)
>  static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
>  {
>  	struct siginfo info;
> +	int ret = 0;
>  
>  	pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n",
>  		 fault_name(esr), esr, addr);
> @@ -508,7 +509,7 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
>  	 */
>  	if (IS_ENABLED(CONFIG_ACPI_APEI_SEA)) {
>  		nmi_enter();
> -		ghes_notify_sea();
> +		ret = ghes_notify_sea();
>  		nmi_exit();
>  	}
>  
> @@ -521,7 +522,7 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs)
>  		info.si_addr  = (void __user *)addr;
>  	arm64_notify_die("", regs, &info, esr);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  static const struct fault_info {
> @@ -603,6 +604,20 @@ static const char *fault_name(unsigned int esr)
>  }
>  
>  /*
> + * Handle Synchronous External Aborts that occur in a guest kernel.
> + */

Can you document what the return value here means?

I have no idea what the semantics of ghes_notify_sea() are.

> +int handle_guest_sea(unsigned long addr, unsigned int esr)
> +{
> +	int ret = -ENOENT;
> +
> +	if(IS_ENABLED(CONFIG_ACPI_APEI_SEA)) {
> +		ret = ghes_notify_sea();
> +	}
> +
> +	return ret;
> +}
> +
> +/*
>   * Dispatch a data abort to the relevant handler.
>   */
>  asmlinkage void __exception do_mem_abort(unsigned long addr, unsigned int esr,
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 230b095..81eabc6 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -810,17 +810,18 @@ static int ghes_notify_sci(struct notifier_block *this,
>  #ifdef CONFIG_ACPI_APEI_SEA
>  static LIST_HEAD(ghes_sea);
>  
> -void ghes_notify_sea(void)
> +int ghes_notify_sea(void)
>  {
>  	struct ghes *ghes;
> +	int ret = -ENOENT;
>  
> -	/*
> -	 * synchronize_rcu() will wait for nmi_exit(), so no need to
> -	 * rcu_read_lock().
> -	 */
> +	rcu_read_lock();
>  	list_for_each_entry_rcu(ghes, &ghes_sea, list) {
> -		ghes_proc(ghes);
> +		if(!ghes_proc(ghes))
> +			ret = 0;
>  	}
> +	rcu_read_unlock();
> +	return ret;
>  }
>  
>  static void ghes_sea_add(struct ghes *ghes)
> diff --git a/include/acpi/ghes.h b/include/acpi/ghes.h
> index 18bc935..2a727dc 100644
> --- a/include/acpi/ghes.h
> +++ b/include/acpi/ghes.h
> @@ -99,6 +99,6 @@ static inline void *acpi_hest_generic_data_payload(struct acpi_hest_generic_data
>  		gdata + 1;
>  }
>  
> -void ghes_notify_sea(void);
> +int ghes_notify_sea(void);
>  
>  #endif /* GHES_H */
> -- 
> Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project.
> 

Thanks,
-Christoffer