xen-devel.lists.xenproject.org archive mirror
 help / color / mirror / Atom feed
* [PATCH] Remove support for ThumbEE
@ 2021-04-13  8:24 Michal Orzel
  2021-04-13  9:07 ` Julien Grall
  0 siblings, 1 reply; 6+ messages in thread
From: Michal Orzel @ 2021-04-13  8:24 UTC (permalink / raw)
  To: xen-devel
  Cc: Stefano Stabellini, Julien Grall, Volodymyr Babchuk,
	bertrand.marquis, wei.chen

ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
In 2011 ARM deprecated any use of the ThumbEE instruction set.

This feature is untested and as per my understanding
there are no reported users for it.

Remove all the bits related to it.

Signed-off-by: Michal Orzel <michal.orzel@arm.com>
---
 xen/arch/arm/cpufeature.c        |  3 +++
 xen/arch/arm/domain.c            | 12 ------------
 xen/arch/arm/setup.c             |  3 +--
 xen/include/asm-arm/cpregs.h     |  6 ------
 xen/include/asm-arm/cpufeature.h |  1 -
 xen/include/asm-arm/domain.h     |  1 -
 6 files changed, 4 insertions(+), 22 deletions(-)

diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
index 1d88783809..82265a72f4 100644
--- a/xen/arch/arm/cpufeature.c
+++ b/xen/arch/arm/cpufeature.c
@@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
     guest_cpuinfo.pfr32.ras = 0;
     guest_cpuinfo.pfr32.ras_frac = 0;
 
+    /* Hide ThumbEE support */
+    guest_cpuinfo.pfr32.thumbee = 0;
+
     return 0;
 }
 /*
diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
index bdd3d3e5b5..d12903407f 100644
--- a/xen/arch/arm/domain.c
+++ b/xen/arch/arm/domain.c
@@ -116,12 +116,6 @@ static void ctxt_switch_from(struct vcpu *p)
     p->arch.cntkctl = READ_SYSREG32(CNTKCTL_EL1);
     virt_timer_save(p);
 
-    if ( is_32bit_domain(p->domain) && cpu_has_thumbee )
-    {
-        p->arch.teecr = READ_SYSREG32(TEECR32_EL1);
-        p->arch.teehbr = READ_SYSREG32(TEEHBR32_EL1);
-    }
-
 #ifdef CONFIG_ARM_32
     p->arch.joscr = READ_CP32(JOSCR);
     p->arch.jmcr = READ_CP32(JMCR);
@@ -255,12 +249,6 @@ static void ctxt_switch_to(struct vcpu *n)
     WRITE_SYSREG(n->arch.tpidrro_el0, TPIDRRO_EL0);
     WRITE_SYSREG(n->arch.tpidr_el1, TPIDR_EL1);
 
-    if ( is_32bit_domain(n->domain) && cpu_has_thumbee )
-    {
-        WRITE_SYSREG32(n->arch.teecr, TEECR32_EL1);
-        WRITE_SYSREG32(n->arch.teehbr, TEEHBR32_EL1);
-    }
-
 #ifdef CONFIG_ARM_32
     WRITE_CP32(n->arch.joscr, JOSCR);
     WRITE_CP32(n->arch.jmcr, JMCR);
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 9ba2f267f6..76841262e3 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -165,12 +165,11 @@ static void __init processor_id(void)
         printk("32-bit Execution:\n");
         printk("  Processor Features: %"PRIregister":%"PRIregister"\n",
                boot_cpu_data.pfr32.bits[0], boot_cpu_data.pfr32.bits[1]);
-        printk("    Instruction Sets:%s%s%s%s%s%s\n",
+        printk("    Instruction Sets:%s%s%s%s%s\n",
                cpu_has_aarch32 ? " AArch32" : "",
                cpu_has_arm ? " A32" : "",
                cpu_has_thumb ? " Thumb" : "",
                cpu_has_thumb2 ? " Thumb-2" : "",
-               cpu_has_thumbee ? " ThumbEE" : "",
                cpu_has_jazelle ? " Jazelle" : "");
         printk("    Extensions:%s%s\n",
                cpu_has_gentimer ? " GenericTimer" : "",
diff --git a/xen/include/asm-arm/cpregs.h b/xen/include/asm-arm/cpregs.h
index 6daf2b1a30..2966c21708 100644
--- a/xen/include/asm-arm/cpregs.h
+++ b/xen/include/asm-arm/cpregs.h
@@ -87,13 +87,9 @@
 #define DBGOSDLR        p14,0,c1,c3,4   /* OS Double Lock */
 #define DBGPRCR         p14,0,c1,c4,4   /* Debug Power Control Register */
 
-/* CP14 CR0: */
-#define TEECR           p14,6,c0,c0,0   /* ThumbEE Configuration Register */
-
 /* CP14 CR1: */
 #define DBGDRAR64       p14,0,c1        /* Debug ROM Address Register (64-bit access) */
 #define DBGDRAR         p14,0,c1,c0,0   /* Debug ROM Address Register (32-bit access) */
-#define TEEHBR          p14,6,c1,c0,0   /* ThumbEE Handler Base Register */
 #define JOSCR           p14,7,c1,c0,0   /* Jazelle OS Control Register */
 
 /* CP14 CR2: */
@@ -344,8 +340,6 @@
 #define SCTLR_EL1               SCTLR
 #define SCTLR_EL2               HSCTLR
 #define TCR_EL1                 TTBCR
-#define TEECR32_EL1             TEECR
-#define TEEHBR32_EL1            TEEHBR
 #define TPIDRRO_EL0             TPIDRURO
 #define TPIDR_EL0               TPIDRURW
 #define TPIDR_EL1               TPIDRPRW
diff --git a/xen/include/asm-arm/cpufeature.h b/xen/include/asm-arm/cpufeature.h
index ba48db3eac..f02ae8fde2 100644
--- a/xen/include/asm-arm/cpufeature.h
+++ b/xen/include/asm-arm/cpufeature.h
@@ -27,7 +27,6 @@
 #define cpu_has_thumb     (boot_cpu_feature32(thumb) >= 1)
 #define cpu_has_thumb2    (boot_cpu_feature32(thumb) >= 3)
 #define cpu_has_jazelle   (boot_cpu_feature32(jazelle) > 0)
-#define cpu_has_thumbee   (boot_cpu_feature32(thumbee) == 1)
 #define cpu_has_aarch32   (cpu_has_arm || cpu_has_thumb)
 
 #ifdef CONFIG_ARM_32
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 1da90f207d..d5080a6df6 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -167,7 +167,6 @@ struct arch_vcpu
     /* HYP configuration */
     register_t hcr_el2;
 
-    uint32_t teecr, teehbr; /* ThumbEE, 32-bit guests only */
 #ifdef CONFIG_ARM_32
     /*
      * ARMv8 only supports a trivial implementation on Jazelle when in AArch32
-- 
2.29.0



^ permalink raw reply related	[flat|nested] 6+ messages in thread

* Re: [PATCH] Remove support for ThumbEE
  2021-04-13  8:24 [PATCH] Remove support for ThumbEE Michal Orzel
@ 2021-04-13  9:07 ` Julien Grall
  2021-04-13  9:32   ` Michal Orzel
  0 siblings, 1 reply; 6+ messages in thread
From: Julien Grall @ 2021-04-13  9:07 UTC (permalink / raw)
  To: Michal Orzel, xen-devel
  Cc: Stefano Stabellini, Volodymyr Babchuk, bertrand.marquis, wei.chen

Hi Michal,

On 13/04/2021 09:24, Michal Orzel wrote:
> ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
> In 2011 ARM deprecated any use of the ThumbEE instruction set.

This doesn't mean this is not present in any CPU. In fact, in the same 
section (see A2.10 in ARM DDI 0406C.d):

"ThumbEE is both the name of the instruction set and the name of the 
extension that provides support for that
instruction set. The ThumbEE Extension is:
   - Required in implementations of the ARMv7-A profile.
   - Optional in implementations of the ARMv7-R profile.
"

> 
> This feature is untested and as per my understanding
> there are no reported users for it. >
> Remove all the bits related to it.
> 
> Signed-off-by: Michal Orzel <michal.orzel@arm.com> > ---
>   xen/arch/arm/cpufeature.c        |  3 +++
>   xen/arch/arm/domain.c            | 12 ------------
>   xen/arch/arm/setup.c             |  3 +--
>   xen/include/asm-arm/cpregs.h     |  6 ------
>   xen/include/asm-arm/cpufeature.h |  1 -
>   xen/include/asm-arm/domain.h     |  1 -
>   6 files changed, 4 insertions(+), 22 deletions(-)
> 
> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
> index 1d88783809..82265a72f4 100644
> --- a/xen/arch/arm/cpufeature.c
> +++ b/xen/arch/arm/cpufeature.c
> @@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
>       guest_cpuinfo.pfr32.ras = 0;
>       guest_cpuinfo.pfr32.ras_frac = 0;
>   
> +    /* Hide ThumbEE support */
> +    guest_cpuinfo.pfr32.thumbee = 0;

Even if you hide the feature from the guest, the registers are still 
accessible. So you are not removing support but just opening a potential 
security hole as the registers now gets shared...

Looking at the spec, it doesn't look like it is possible to trap them.

In any case, the number of registers to save/restore is pretty limited. 
So I don't see the problem to keep the code around. It doesn't mean the 
feature is working, it just means we properly keep the domain isolated 
from each other.

Cheers,

-- 
Julien Grall


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] Remove support for ThumbEE
  2021-04-13  9:07 ` Julien Grall
@ 2021-04-13  9:32   ` Michal Orzel
  2021-04-13  9:42     ` Julien Grall
  0 siblings, 1 reply; 6+ messages in thread
From: Michal Orzel @ 2021-04-13  9:32 UTC (permalink / raw)
  To: Julien Grall, xen-devel
  Cc: Stefano Stabellini, Volodymyr Babchuk, bertrand.marquis, wei.chen

Hi Julien,

On 13.04.2021 11:07, Julien Grall wrote:
> Hi Michal,
> 
> On 13/04/2021 09:24, Michal Orzel wrote:
>> ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
>> In 2011 ARM deprecated any use of the ThumbEE instruction set.
> 
> This doesn't mean this is not present in any CPU. In fact, in the same section (see A2.10 in ARM DDI 0406C.d):
> 
> "ThumbEE is both the name of the instruction set and the name of the extension that provides support for that
> instruction set. The ThumbEE Extension is:
>   - Required in implementations of the ARMv7-A profile.
>   - Optional in implementations of the ARMv7-R profile.
> "
> 
>>
>> This feature is untested and as per my understanding
>> there are no reported users for it. >
>> Remove all the bits related to it.
>>
>> Signed-off-by: Michal Orzel <michal.orzel@arm.com> > ---
>>   xen/arch/arm/cpufeature.c        |  3 +++
>>   xen/arch/arm/domain.c            | 12 ------------
>>   xen/arch/arm/setup.c             |  3 +--
>>   xen/include/asm-arm/cpregs.h     |  6 ------
>>   xen/include/asm-arm/cpufeature.h |  1 -
>>   xen/include/asm-arm/domain.h     |  1 -
>>   6 files changed, 4 insertions(+), 22 deletions(-)
>>
>> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
>> index 1d88783809..82265a72f4 100644
>> --- a/xen/arch/arm/cpufeature.c
>> +++ b/xen/arch/arm/cpufeature.c
>> @@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
>>       guest_cpuinfo.pfr32.ras = 0;
>>       guest_cpuinfo.pfr32.ras_frac = 0;
>>   +    /* Hide ThumbEE support */
>> +    guest_cpuinfo.pfr32.thumbee = 0;
> 
> Even if you hide the feature from the guest, the registers are still accessible. So you are not removing support but just opening a potential security hole as the registers now gets shared...
> 
> Looking at the spec, it doesn't look like it is possible to trap them.
Looking at the spec for ARMv7A/R:
https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/System-Control-Registers-in-a-VMSA-implementation/VMSA-System-control-registers-descriptions--in-register-order/HSTR--Hyp-System-Trap-Register--Virtualization-Extensions
we can trap Thumbee operations.
This means that we will not open the security hole.

> 
> In any case, the number of registers to save/restore is pretty limited. So I don't see the problem to keep the code around. It doesn't mean the feature is working, it just means we properly keep the domain isolated from each other.
> 
> Cheers,
> 

Cheers,
Michal


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] Remove support for ThumbEE
  2021-04-13  9:32   ` Michal Orzel
@ 2021-04-13  9:42     ` Julien Grall
  2021-04-13  9:59       ` Michal Orzel
  0 siblings, 1 reply; 6+ messages in thread
From: Julien Grall @ 2021-04-13  9:42 UTC (permalink / raw)
  To: Michal Orzel, xen-devel
  Cc: Stefano Stabellini, Volodymyr Babchuk, bertrand.marquis, wei.chen



On 13/04/2021 10:32, Michal Orzel wrote:
> Hi Julien,
> 
> On 13.04.2021 11:07, Julien Grall wrote:
>> Hi Michal,
>>
>> On 13/04/2021 09:24, Michal Orzel wrote:
>>> ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
>>> In 2011 ARM deprecated any use of the ThumbEE instruction set.
>>
>> This doesn't mean this is not present in any CPU. In fact, in the same section (see A2.10 in ARM DDI 0406C.d):
>>
>> "ThumbEE is both the name of the instruction set and the name of the extension that provides support for that
>> instruction set. The ThumbEE Extension is:
>>    - Required in implementations of the ARMv7-A profile.
>>    - Optional in implementations of the ARMv7-R profile.
>> "
>>
>>>
>>> This feature is untested and as per my understanding
>>> there are no reported users for it. >
>>> Remove all the bits related to it.
>>>
>>> Signed-off-by: Michal Orzel <michal.orzel@arm.com> > ---
>>>    xen/arch/arm/cpufeature.c        |  3 +++
>>>    xen/arch/arm/domain.c            | 12 ------------
>>>    xen/arch/arm/setup.c             |  3 +--
>>>    xen/include/asm-arm/cpregs.h     |  6 ------
>>>    xen/include/asm-arm/cpufeature.h |  1 -
>>>    xen/include/asm-arm/domain.h     |  1 -
>>>    6 files changed, 4 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
>>> index 1d88783809..82265a72f4 100644
>>> --- a/xen/arch/arm/cpufeature.c
>>> +++ b/xen/arch/arm/cpufeature.c
>>> @@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
>>>        guest_cpuinfo.pfr32.ras = 0;
>>>        guest_cpuinfo.pfr32.ras_frac = 0;
>>>    +    /* Hide ThumbEE support */
>>> +    guest_cpuinfo.pfr32.thumbee = 0;
>>
>> Even if you hide the feature from the guest, the registers are still accessible. So you are not removing support but just opening a potential security hole as the registers now gets shared...
>>
>> Looking at the spec, it doesn't look like it is possible to trap them.
> Looking at the spec for ARMv7A/R:
> https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/System-Control-Registers-in-a-VMSA-implementation/VMSA-System-control-registers-descriptions--in-register-order/HSTR--Hyp-System-Trap-Register--Virtualization-Extensions
> we can trap Thumbee operations.
> This means that we will not open the security hole.

That's for pointing that out. However, I am not still not sure why you 
want to drop the code. Yes this is technically untested, but:
   1) The change is very small
   2) There are CPU out there supporting it (it is mandated after all).

-- 
Julien Grall


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] Remove support for ThumbEE
  2021-04-13  9:42     ` Julien Grall
@ 2021-04-13  9:59       ` Michal Orzel
  2021-04-13 10:10         ` Julien Grall
  0 siblings, 1 reply; 6+ messages in thread
From: Michal Orzel @ 2021-04-13  9:59 UTC (permalink / raw)
  To: Julien Grall, xen-devel
  Cc: Stefano Stabellini, Volodymyr Babchuk, bertrand.marquis, wei.chen



On 13.04.2021 11:42, Julien Grall wrote:
> 
> 
> On 13/04/2021 10:32, Michal Orzel wrote:
>> Hi Julien,
>>
>> On 13.04.2021 11:07, Julien Grall wrote:
>>> Hi Michal,
>>>
>>> On 13/04/2021 09:24, Michal Orzel wrote:
>>>> ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
>>>> In 2011 ARM deprecated any use of the ThumbEE instruction set.
>>>
>>> This doesn't mean this is not present in any CPU. In fact, in the same section (see A2.10 in ARM DDI 0406C.d):
>>>
>>> "ThumbEE is both the name of the instruction set and the name of the extension that provides support for that
>>> instruction set. The ThumbEE Extension is:
>>>    - Required in implementations of the ARMv7-A profile.
>>>    - Optional in implementations of the ARMv7-R profile.
>>> "
>>>
>>>>
>>>> This feature is untested and as per my understanding
>>>> there are no reported users for it. >
>>>> Remove all the bits related to it.
>>>>
>>>> Signed-off-by: Michal Orzel <michal.orzel@arm.com> > ---
>>>>    xen/arch/arm/cpufeature.c        |  3 +++
>>>>    xen/arch/arm/domain.c            | 12 ------------
>>>>    xen/arch/arm/setup.c             |  3 +--
>>>>    xen/include/asm-arm/cpregs.h     |  6 ------
>>>>    xen/include/asm-arm/cpufeature.h |  1 -
>>>>    xen/include/asm-arm/domain.h     |  1 -
>>>>    6 files changed, 4 insertions(+), 22 deletions(-)
>>>>
>>>> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
>>>> index 1d88783809..82265a72f4 100644
>>>> --- a/xen/arch/arm/cpufeature.c
>>>> +++ b/xen/arch/arm/cpufeature.c
>>>> @@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
>>>>        guest_cpuinfo.pfr32.ras = 0;
>>>>        guest_cpuinfo.pfr32.ras_frac = 0;
>>>>    +    /* Hide ThumbEE support */
>>>> +    guest_cpuinfo.pfr32.thumbee = 0;
>>>
>>> Even if you hide the feature from the guest, the registers are still accessible. So you are not removing support but just opening a potential security hole as the registers now gets shared...
>>>
>>> Looking at the spec, it doesn't look like it is possible to trap them.
>> Looking at the spec for ARMv7A/R:
>> https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/System-Control-Registers-in-a-VMSA-implementation/VMSA-System-control-registers-descriptions--in-register-order/HSTR--Hyp-System-Trap-Register--Virtualization-Extensions
>> we can trap Thumbee operations.
>> This means that we will not open the security hole.
> 
> That's for pointing that out. However, I am not still not sure why you want to drop the code. Yes this is technically untested, but:
>   1) The change is very small
>   2) There are CPU out there supporting it (it is mandated after all).
> 
I wanted to drop the support for thumbee due to the following reasons:
-it is untested
-it is deprecated
-no reported users for this feature
-KVM did that

If you think we should not do this, then I am ok to abandon this patch.


^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [PATCH] Remove support for ThumbEE
  2021-04-13  9:59       ` Michal Orzel
@ 2021-04-13 10:10         ` Julien Grall
  0 siblings, 0 replies; 6+ messages in thread
From: Julien Grall @ 2021-04-13 10:10 UTC (permalink / raw)
  To: Michal Orzel, xen-devel
  Cc: Stefano Stabellini, Volodymyr Babchuk, bertrand.marquis, wei.chen



On 13/04/2021 10:59, Michal Orzel wrote:
> 
> 
> On 13.04.2021 11:42, Julien Grall wrote:
>>
>>
>> On 13/04/2021 10:32, Michal Orzel wrote:
>>> Hi Julien,
>>>
>>> On 13.04.2021 11:07, Julien Grall wrote:
>>>> Hi Michal,
>>>>
>>>> On 13/04/2021 09:24, Michal Orzel wrote:
>>>>> ThumbEE(T32EE) was introduced in ARMv7 and removed in ARMv8.
>>>>> In 2011 ARM deprecated any use of the ThumbEE instruction set.
>>>>
>>>> This doesn't mean this is not present in any CPU. In fact, in the same section (see A2.10 in ARM DDI 0406C.d):
>>>>
>>>> "ThumbEE is both the name of the instruction set and the name of the extension that provides support for that
>>>> instruction set. The ThumbEE Extension is:
>>>>     - Required in implementations of the ARMv7-A profile.
>>>>     - Optional in implementations of the ARMv7-R profile.
>>>> "
>>>>
>>>>>
>>>>> This feature is untested and as per my understanding
>>>>> there are no reported users for it. >
>>>>> Remove all the bits related to it.
>>>>>
>>>>> Signed-off-by: Michal Orzel <michal.orzel@arm.com> > ---
>>>>>     xen/arch/arm/cpufeature.c        |  3 +++
>>>>>     xen/arch/arm/domain.c            | 12 ------------
>>>>>     xen/arch/arm/setup.c             |  3 +--
>>>>>     xen/include/asm-arm/cpregs.h     |  6 ------
>>>>>     xen/include/asm-arm/cpufeature.h |  1 -
>>>>>     xen/include/asm-arm/domain.h     |  1 -
>>>>>     6 files changed, 4 insertions(+), 22 deletions(-)
>>>>>
>>>>> diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
>>>>> index 1d88783809..82265a72f4 100644
>>>>> --- a/xen/arch/arm/cpufeature.c
>>>>> +++ b/xen/arch/arm/cpufeature.c
>>>>> @@ -209,6 +209,9 @@ static int __init create_guest_cpuinfo(void)
>>>>>         guest_cpuinfo.pfr32.ras = 0;
>>>>>         guest_cpuinfo.pfr32.ras_frac = 0;
>>>>>     +    /* Hide ThumbEE support */
>>>>> +    guest_cpuinfo.pfr32.thumbee = 0;
>>>>
>>>> Even if you hide the feature from the guest, the registers are still accessible. So you are not removing support but just opening a potential security hole as the registers now gets shared...
>>>>
>>>> Looking at the spec, it doesn't look like it is possible to trap them.
>>> Looking at the spec for ARMv7A/R:
>>> https://developer.arm.com/documentation/ddi0406/c/System-Level-Architecture/System-Control-Registers-in-a-VMSA-implementation/VMSA-System-control-registers-descriptions--in-register-order/HSTR--Hyp-System-Trap-Register--Virtualization-Extensions
>>> we can trap Thumbee operations.
>>> This means that we will not open the security hole.
>>
>> That's for pointing that out. However, I am not still not sure why you want to drop the code. Yes this is technically untested, but:
>>    1) The change is very small
>>    2) There are CPU out there supporting it (it is mandated after all).
>>
> I wanted to drop the support for thumbee due to the following reasons:
> -it is untested
> -it is deprecated

Deprecated only means new code should avoid to use the instruction set. 
But it is still present for existing code until they are migrated to a 
newer instruction set.

However, as I pointed out only the instruction set is deprecated. The 
extension itself is mandated by Armv7-A.

> -no reported users for this feature
We probably only see the tip of the iceberg in term of the users. If the 
feature/pain is quite small to the community, then we should try to not 
drop feature.

> -KVM did that

Well, KVM fully dropped 32-bit support. But I am not yet in favor of 
that in Xen.

> 
> If you think we should not do this, then I am ok to abandon this patch.

Based on the information you provided, I think we should keep support.

Cheers,

-- 
Julien Grall


^ permalink raw reply	[flat|nested] 6+ messages in thread

end of thread, other threads:[~2021-04-13 10:10 UTC | newest]

Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-13  8:24 [PATCH] Remove support for ThumbEE Michal Orzel
2021-04-13  9:07 ` Julien Grall
2021-04-13  9:32   ` Michal Orzel
2021-04-13  9:42     ` Julien Grall
2021-04-13  9:59       ` Michal Orzel
2021-04-13 10:10         ` Julien Grall

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).