[Xen-devel] [PATCH v2 2/7] xen/arm: Remove flush_xen_text_tlb_local()

Julien Grall posted 7 patches 1 year, 11 months ago

[Xen-devel] [PATCH v2 2/7] xen/arm: Remove flush_xen_text_tlb_local()

Posted by Julien Grall 1 year, 11 months ago
The function flush_xen_text_tlb_local() has been misused and will result
to invalidate the instruction cache more than necessary.

For instance, there are no need to invalidate the instruction cache if
we are setting SCTLR_EL2.WXN.

There are effectively only one caller (i.e free_init_memory() would
who need to invalidate the instruction cache.

So rather than keeping around the function flush_xen_text_tlb_local()
around, replace it with call to flush_xen_tlb_local() and explicitely
flush the cache when necessary.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>

---
    Changes in v2:
        - Add Andrii's reviewed-by
---
 xen/arch/arm/mm.c                | 17 ++++++++++++++---
 xen/include/asm-arm/arm32/page.h | 23 +++++++++--------------
 xen/include/asm-arm/arm64/page.h | 21 +++++----------------
 3 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 93ad118183..dfbe39c70a 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -610,8 +610,12 @@ void __init remove_early_mappings(void)
 static void xen_pt_enforce_wnx(void)
 {
     WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_WXN, SCTLR_EL2);
-    /* Flush everything after setting WXN bit. */
-    flush_xen_text_tlb_local();
+    /*
+     * The TLBs may cache SCTLR_EL2.WXN. So ensure it is synchronized
+     * before flushing the TLBs.
+     */
+    isb();
+    flush_xen_data_tlb_local();
 }
 
 extern void switch_ttbr(uint64_t ttbr);
@@ -1123,7 +1127,7 @@ static void set_pte_flags_on_range(const char *p, unsigned long l, enum mg mg)
         }
         write_pte(xen_xenmap + i, pte);
     }
-    flush_xen_text_tlb_local();
+    flush_xen_data_tlb_local();
 }
 
 /* Release all __init and __initdata ranges to be reused */
@@ -1136,6 +1140,13 @@ void free_init_memory(void)
     uint32_t *p;
 
     set_pte_flags_on_range(__init_begin, len, mg_rw);
+
+    /*
+     * From now on, init will not be used for execution anymore,
+     * so nuke the instruction cache to remove entries related to init.
+     */
+    invalidate_icache_local();
+
 #ifdef CONFIG_ARM_32
     /* udf instruction i.e (see A8.8.247 in ARM DDI 0406C.c) */
     insn = 0xe7f000f0;
diff --git a/xen/include/asm-arm/arm32/page.h b/xen/include/asm-arm/arm32/page.h
index ea4b312c70..40a77daa9d 100644
--- a/xen/include/asm-arm/arm32/page.h
+++ b/xen/include/asm-arm/arm32/page.h
@@ -46,24 +46,19 @@ static inline void invalidate_icache(void)
 }
 
 /*
- * Flush all hypervisor mappings from the TLB and branch predictor of
- * the local processor.
- *
- * This is needed after changing Xen code mappings.
- *
- * The caller needs to issue the necessary DSB and D-cache flushes
- * before calling flush_xen_text_tlb.
+ * Invalidate all instruction caches on the local processor to PoU.
+ * We also need to flush the branch predictor for ARMv7 as it may be
+ * architecturally visible to the software (see B2.2.4 in ARM DDI 0406C.b).
  */
-static inline void flush_xen_text_tlb_local(void)
+static inline void invalidate_icache_local(void)
 {
     asm volatile (
-        "isb;"                        /* Ensure synchronization with previous changes to text */
-        CMD_CP32(TLBIALLH)            /* Flush hypervisor TLB */
-        CMD_CP32(ICIALLU)             /* Flush I-cache */
-        CMD_CP32(BPIALL)              /* Flush branch predictor */
-        "dsb;"                        /* Ensure completion of TLB+BP flush */
-        "isb;"
+        CMD_CP32(ICIALLU)       /* Flush I-cache. */
+        CMD_CP32(BPIALL)        /* Flush branch predictor. */
         : : : "memory");
+
+    dsb(nsh);                   /* Ensure completion of the flush I-cache */
+    isb();                      /* Synchronize fetched instruction stream. */
 }
 
 /*
diff --git a/xen/include/asm-arm/arm64/page.h b/xen/include/asm-arm/arm64/page.h
index 23d778154d..6c36d0210f 100644
--- a/xen/include/asm-arm/arm64/page.h
+++ b/xen/include/asm-arm/arm64/page.h
@@ -37,23 +37,12 @@ static inline void invalidate_icache(void)
     isb();
 }
 
-/*
- * Flush all hypervisor mappings from the TLB of the local processor.
- *
- * This is needed after changing Xen code mappings.
- *
- * The caller needs to issue the necessary DSB and D-cache flushes
- * before calling flush_xen_text_tlb.
- */
-static inline void flush_xen_text_tlb_local(void)
+/* Invalidate all instruction caches on the local processor to PoU */
+static inline void invalidate_icache_local(void)
 {
-    asm volatile (
-        "isb;"       /* Ensure synchronization with previous changes to text */
-        "tlbi   alle2;"                 /* Flush hypervisor TLB */
-        "ic     iallu;"                 /* Flush I-cache */
-        "dsb    sy;"                    /* Ensure completion of TLB flush */
-        "isb;"
-        : : : "memory");
+    asm volatile ("ic iallu");
+    dsb(nsh);               /* Ensure completion of the I-cache flush */
+    isb();
 }
 
 /*
-- 
2.11.0


_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v2 2/7] xen/arm: Remove flush_xen_text_tlb_local()

Posted by Stefano Stabellini 1 year, 11 months ago
On Wed, 8 May 2019, Julien Grall wrote:
> The function flush_xen_text_tlb_local() has been misused and will result
> to invalidate the instruction cache more than necessary.
> 
> For instance, there are no need to invalidate the instruction cache if
                       ^ is


> we are setting SCTLR_EL2.WXN.
> 
> There are effectively only one caller (i.e free_init_memory() would
        ^ is

> who need to invalidate the instruction cache.
  ^ would who / who would

> 
> So rather than keeping around the function flush_xen_text_tlb_local()
> around, replace it with call to flush_xen_tlb_local() and explicitely
  ^ remove


> flush the cache when necessary.
> 
> Signed-off-by: Julien Grall <julien.grall@arm.com>
> Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
> 
> ---
>     Changes in v2:
>         - Add Andrii's reviewed-by
> ---
>  xen/arch/arm/mm.c                | 17 ++++++++++++++---
>  xen/include/asm-arm/arm32/page.h | 23 +++++++++--------------
>  xen/include/asm-arm/arm64/page.h | 21 +++++----------------
>  3 files changed, 28 insertions(+), 33 deletions(-)
> 
> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
> index 93ad118183..dfbe39c70a 100644
> --- a/xen/arch/arm/mm.c
> +++ b/xen/arch/arm/mm.c
> @@ -610,8 +610,12 @@ void __init remove_early_mappings(void)
>  static void xen_pt_enforce_wnx(void)
>  {
>      WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_WXN, SCTLR_EL2);
> -    /* Flush everything after setting WXN bit. */
> -    flush_xen_text_tlb_local();
> +    /*
> +     * The TLBs may cache SCTLR_EL2.WXN. So ensure it is synchronized
> +     * before flushing the TLBs.
> +     */
> +    isb();
> +    flush_xen_data_tlb_local();
>  }
>  
>  extern void switch_ttbr(uint64_t ttbr);
> @@ -1123,7 +1127,7 @@ static void set_pte_flags_on_range(const char *p, unsigned long l, enum mg mg)
>          }
>          write_pte(xen_xenmap + i, pte);
>      }
> -    flush_xen_text_tlb_local();
> +    flush_xen_data_tlb_local();

I think it would make sense to move the remaining call to
flush_xen_data_tlb_local from set_pte_flags_on_range to free_init_memory
before the call to invalidate_icache_local. What do you think?


>  }
>  
>  /* Release all __init and __initdata ranges to be reused */
> @@ -1136,6 +1140,13 @@ void free_init_memory(void)
>      uint32_t *p;
>  
>      set_pte_flags_on_range(__init_begin, len, mg_rw);
> +
> +    /*
> +     * From now on, init will not be used for execution anymore,
> +     * so nuke the instruction cache to remove entries related to init.
> +     */
> +    invalidate_icache_local();
> +
>  #ifdef CONFIG_ARM_32
>      /* udf instruction i.e (see A8.8.247 in ARM DDI 0406C.c) */
>      insn = 0xe7f000f0;
> diff --git a/xen/include/asm-arm/arm32/page.h b/xen/include/asm-arm/arm32/page.h
> index ea4b312c70..40a77daa9d 100644
> --- a/xen/include/asm-arm/arm32/page.h
> +++ b/xen/include/asm-arm/arm32/page.h
> @@ -46,24 +46,19 @@ static inline void invalidate_icache(void)
>  }
>  
>  /*
> - * Flush all hypervisor mappings from the TLB and branch predictor of
> - * the local processor.
> - *
> - * This is needed after changing Xen code mappings.
> - *
> - * The caller needs to issue the necessary DSB and D-cache flushes
> - * before calling flush_xen_text_tlb.
> + * Invalidate all instruction caches on the local processor to PoU.
> + * We also need to flush the branch predictor for ARMv7 as it may be
> + * architecturally visible to the software (see B2.2.4 in ARM DDI 0406C.b).
>   */
> -static inline void flush_xen_text_tlb_local(void)
> +static inline void invalidate_icache_local(void)
>  {
>      asm volatile (
> -        "isb;"                        /* Ensure synchronization with previous changes to text */
> -        CMD_CP32(TLBIALLH)            /* Flush hypervisor TLB */
> -        CMD_CP32(ICIALLU)             /* Flush I-cache */
> -        CMD_CP32(BPIALL)              /* Flush branch predictor */
> -        "dsb;"                        /* Ensure completion of TLB+BP flush */
> -        "isb;"
> +        CMD_CP32(ICIALLU)       /* Flush I-cache. */
> +        CMD_CP32(BPIALL)        /* Flush branch predictor. */
>          : : : "memory");
> +
> +    dsb(nsh);                   /* Ensure completion of the flush I-cache */
> +    isb();                      /* Synchronize fetched instruction stream. */
>  }
>  
>  /*
> diff --git a/xen/include/asm-arm/arm64/page.h b/xen/include/asm-arm/arm64/page.h
> index 23d778154d..6c36d0210f 100644
> --- a/xen/include/asm-arm/arm64/page.h
> +++ b/xen/include/asm-arm/arm64/page.h
> @@ -37,23 +37,12 @@ static inline void invalidate_icache(void)
>      isb();
>  }
>  
> -/*
> - * Flush all hypervisor mappings from the TLB of the local processor.
> - *
> - * This is needed after changing Xen code mappings.
> - *
> - * The caller needs to issue the necessary DSB and D-cache flushes
> - * before calling flush_xen_text_tlb.
> - */
> -static inline void flush_xen_text_tlb_local(void)
> +/* Invalidate all instruction caches on the local processor to PoU */
> +static inline void invalidate_icache_local(void)
>  {
> -    asm volatile (
> -        "isb;"       /* Ensure synchronization with previous changes to text */
> -        "tlbi   alle2;"                 /* Flush hypervisor TLB */
> -        "ic     iallu;"                 /* Flush I-cache */
> -        "dsb    sy;"                    /* Ensure completion of TLB flush */
> -        "isb;"
> -        : : : "memory");
> +    asm volatile ("ic iallu");
> +    dsb(nsh);               /* Ensure completion of the I-cache flush */
> +    isb();
>  }
>  
>  /*
> -- 
> 2.11.0
> 

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel

Re: [Xen-devel] [PATCH v2 2/7] xen/arm: Remove flush_xen_text_tlb_local()

Posted by Julien Grall 1 year, 11 months ago
Hi,

On 09/05/2019 21:03, Stefano Stabellini wrote:
> On Wed, 8 May 2019, Julien Grall wrote:
>> The function flush_xen_text_tlb_local() has been misused and will result
>> to invalidate the instruction cache more than necessary.
>>
>> For instance, there are no need to invalidate the instruction cache if
>                         ^ is
> 
> 
>> we are setting SCTLR_EL2.WXN.
>>
>> There are effectively only one caller (i.e free_init_memory() would
>          ^ is
> 
>> who need to invalidate the instruction cache.
>    ^ would who / who would
> 
>>
>> So rather than keeping around the function flush_xen_text_tlb_local()
>> around, replace it with call to flush_xen_tlb_local() and explicitely
>    ^ remove

I will fix the typoes in the next version.

> 
> 
>> flush the cache when necessary.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>> Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
>>
>> ---
>>      Changes in v2:
>>          - Add Andrii's reviewed-by
>> ---
>>   xen/arch/arm/mm.c                | 17 ++++++++++++++---
>>   xen/include/asm-arm/arm32/page.h | 23 +++++++++--------------
>>   xen/include/asm-arm/arm64/page.h | 21 +++++----------------
>>   3 files changed, 28 insertions(+), 33 deletions(-)
>>
>> diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
>> index 93ad118183..dfbe39c70a 100644
>> --- a/xen/arch/arm/mm.c
>> +++ b/xen/arch/arm/mm.c
>> @@ -610,8 +610,12 @@ void __init remove_early_mappings(void)
>>   static void xen_pt_enforce_wnx(void)
>>   {
>>       WRITE_SYSREG32(READ_SYSREG32(SCTLR_EL2) | SCTLR_WXN, SCTLR_EL2);
>> -    /* Flush everything after setting WXN bit. */
>> -    flush_xen_text_tlb_local();
>> +    /*
>> +     * The TLBs may cache SCTLR_EL2.WXN. So ensure it is synchronized
>> +     * before flushing the TLBs.
>> +     */
>> +    isb();
>> +    flush_xen_data_tlb_local();
>>   }
>>   
>>   extern void switch_ttbr(uint64_t ttbr);
>> @@ -1123,7 +1127,7 @@ static void set_pte_flags_on_range(const char *p, unsigned long l, enum mg mg)
>>           }
>>           write_pte(xen_xenmap + i, pte);
>>       }
>> -    flush_xen_text_tlb_local();
>> +    flush_xen_data_tlb_local();
> 
> I think it would make sense to move the remaining call to
> flush_xen_data_tlb_local from set_pte_flags_on_range to free_init_memory
> before the call to invalidate_icache_local. What do you think?

We still need the TLB flush for the two callers. The first one for 
remove all TLBs with the previous permission, the second when the 
mappings are removed from the TLBs.

Today, it is not possible to re-use the virtual address of the init 
section, so it is arguably not necessary. However, I don't want to take 
the chance to introduce potential coherency issues if the TLBs entries 
where still present when re-using the virtual address.

Cheers,

-- 
Julien Grall
_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel