Re: [Xen-devel] [for-4.8][PATCH v2 07/23] xen/arm: traps: Check the P2M before injecting a data/instruction abort

[Stefano Stabellini]

On Thu, 15 Sep 2016, Julien Grall wrote:
> A data/instruction abort may have occurred if another CPU was playing
> with the stage-2 page table when following the break-before-make
> sequence (see D4.7.1 in ARM DDI 0487A.j). Rather than injecting directly
> the fault to the guest, we need to check whether the mapping exists. If
> it exists, return to the guest to replay the instruction.
> 
> Signed-off-by: Julien Grall 

Reviewed-by: Stefano Stabellini 


> ---
> Changes in v2:
> - Remove spurious change
> - Fix typoes
> ---
>  xen/arch/arm/traps.c | 37 -
>  1 file changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
> index 76e4152..d73d29a 100644
> --- a/xen/arch/arm/traps.c
> +++ b/xen/arch/arm/traps.c
> @@ -2405,6 +2405,7 @@ static void do_trap_instr_abort_guest(struct 
> cpu_user_regs *regs,
>  register_t gva = READ_SYSREG(FAR_EL2);
>  uint8_t fsc = hsr.iabt.ifsc & ~FSC_LL_MASK;
>  paddr_t gpa;
> +mfn_t mfn;
>  
>  if ( hpfar_is_valid(hsr.iabt.s1ptw, fsc) )
>  gpa = get_faulting_ipa(gva);
> @@ -2418,6 +2419,11 @@ static void do_trap_instr_abort_guest(struct 
> cpu_user_regs *regs,
>   */
>  flush_tlb_local();
>  
> +/*
> + * We may not be able to translate because someone is
> + * playing with the Stage-2 page table of the domain.
> + * Return to the guest.
> + */
>  rc = gva_to_ipa(gva, , GV2M_READ);
>  if ( rc == -EFAULT )
>  return; /* Try again */
> @@ -2438,8 +2444,17 @@ static void do_trap_instr_abort_guest(struct 
> cpu_user_regs *regs,
>  /* Trap was triggered by mem_access, work here is done */
>  if ( !rc )
>  return;
> +break;
>  }
> -break;
> +case FSC_FLT_TRANS:
> +/*
> + * The PT walk may have failed because someone was playing
> + * with the Stage-2 page table. Walk the Stage-2 PT to check
> + * if the entry exists. If it's the case, return to the guest
> + */
> +mfn = p2m_lookup(current->domain, _gfn(paddr_to_pfn(gpa)), NULL);
> +if ( !mfn_eq(mfn, INVALID_MFN) )
> +return;
>  }
>  
>  inject_iabt_exception(regs, gva, hsr.len);
> @@ -2484,6 +2499,7 @@ static void do_trap_data_abort_guest(struct 
> cpu_user_regs *regs,
>  int rc;
>  mmio_info_t info;
>  uint8_t fsc = hsr.dabt.dfsc & ~FSC_LL_MASK;
> +mfn_t mfn;
>  
>  info.dabt = dabt;
>  #ifdef CONFIG_ARM_32
> @@ -2497,6 +2513,11 @@ static void do_trap_data_abort_guest(struct 
> cpu_user_regs *regs,
>  else
>  {
>  rc = gva_to_ipa(info.gva, , GV2M_READ);
> +/*
> + * We may not be able to translate because someone is
> + * playing with the Stage-2 page table of the domain.
> + * Return to the guest.
> + */
>  if ( rc == -EFAULT )
>  return; /* Try again */
>  }
> @@ -2520,11 +2541,25 @@ static void do_trap_data_abort_guest(struct 
> cpu_user_regs *regs,
>  break;
>  }
>  case FSC_FLT_TRANS:
> +/*
> + * Attempt first to emulate the MMIO as the data abort will
> + * likely happen in an emulated region.
> + */
>  if ( try_handle_mmio(regs, ) )
>  {
>  advance_pc(regs, hsr);
>  return;
>  }
> +
> +/*
> + * The PT walk may have failed because someone was playing
> + * with the Stage-2 page table. Walk the Stage-2 PT to check
> + * if the entry exists. If it's the case, return to the guest
> + */
> +mfn = p2m_lookup(current->domain, _gfn(paddr_to_pfn(info.gpa)), 
> NULL);
> +if ( !mfn_eq(mfn, INVALID_MFN) )
> +return;
> +
>  break;
>  default:
>  gprintk(XENLOG_WARNING, "Unsupported DFSC: HSR=%#x DFSC=%#x\n",
> -- 
> 1.9.1
> 

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[Xen-devel] [for-4.8][PATCH v2 07/23] xen/arm: traps: Check the P2M before injecting a data/instruction abort

[Julien Grall]

A data/instruction abort may have occurred if another CPU was playing
with the stage-2 page table when following the break-before-make
sequence (see D4.7.1 in ARM DDI 0487A.j). Rather than injecting directly
the fault to the guest, we need to check whether the mapping exists. If
it exists, return to the guest to replay the instruction.

Signed-off-by: Julien Grall 

---
Changes in v2:
- Remove spurious change
- Fix typoes
---
 xen/arch/arm/traps.c | 37 -
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 76e4152..d73d29a 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -2405,6 +2405,7 @@ static void do_trap_instr_abort_guest(struct 
cpu_user_regs *regs,
 register_t gva = READ_SYSREG(FAR_EL2);
 uint8_t fsc = hsr.iabt.ifsc & ~FSC_LL_MASK;
 paddr_t gpa;
+mfn_t mfn;
 
 if ( hpfar_is_valid(hsr.iabt.s1ptw, fsc) )
 gpa = get_faulting_ipa(gva);
@@ -2418,6 +2419,11 @@ static void do_trap_instr_abort_guest(struct 
cpu_user_regs *regs,
  */
 flush_tlb_local();
 
+/*
+ * We may not be able to translate because someone is
+ * playing with the Stage-2 page table of the domain.
+ * Return to the guest.
+ */
 rc = gva_to_ipa(gva, , GV2M_READ);
 if ( rc == -EFAULT )
 return; /* Try again */
@@ -2438,8 +2444,17 @@ static void do_trap_instr_abort_guest(struct 
cpu_user_regs *regs,
 /* Trap was triggered by mem_access, work here is done */
 if ( !rc )
 return;
+break;
 }
-break;
+case FSC_FLT_TRANS:
+/*
+ * The PT walk may have failed because someone was playing
+ * with the Stage-2 page table. Walk the Stage-2 PT to check
+ * if the entry exists. If it's the case, return to the guest
+ */
+mfn = p2m_lookup(current->domain, _gfn(paddr_to_pfn(gpa)), NULL);
+if ( !mfn_eq(mfn, INVALID_MFN) )
+return;
 }
 
 inject_iabt_exception(regs, gva, hsr.len);
@@ -2484,6 +2499,7 @@ static void do_trap_data_abort_guest(struct cpu_user_regs 
*regs,
 int rc;
 mmio_info_t info;
 uint8_t fsc = hsr.dabt.dfsc & ~FSC_LL_MASK;
+mfn_t mfn;
 
 info.dabt = dabt;
 #ifdef CONFIG_ARM_32
@@ -2497,6 +2513,11 @@ static void do_trap_data_abort_guest(struct 
cpu_user_regs *regs,
 else
 {
 rc = gva_to_ipa(info.gva, , GV2M_READ);
+/*
+ * We may not be able to translate because someone is
+ * playing with the Stage-2 page table of the domain.
+ * Return to the guest.
+ */
 if ( rc == -EFAULT )
 return; /* Try again */
 }
@@ -2520,11 +2541,25 @@ static void do_trap_data_abort_guest(struct 
cpu_user_regs *regs,
 break;
 }
 case FSC_FLT_TRANS:
+/*
+ * Attempt first to emulate the MMIO as the data abort will
+ * likely happen in an emulated region.
+ */
 if ( try_handle_mmio(regs, ) )
 {
 advance_pc(regs, hsr);
 return;
 }
+
+/*
+ * The PT walk may have failed because someone was playing
+ * with the Stage-2 page table. Walk the Stage-2 PT to check
+ * if the entry exists. If it's the case, return to the guest
+ */
+mfn = p2m_lookup(current->domain, _gfn(paddr_to_pfn(info.gpa)), NULL);
+if ( !mfn_eq(mfn, INVALID_MFN) )
+return;
+
 break;
 default:
 gprintk(XENLOG_WARNING, "Unsupported DFSC: HSR=%#x DFSC=%#x\n",
-- 
1.9.1


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