Re: [edk2] [PATCH] ArmVirtPkg/ArmVirtQemu ARM: work around KVM limitations in LTO build
On 06/04/18 17:30, Ard Biesheuvel wrote:
> On 4 June 2018 at 17:18, Laszlo Ersek wrote:
>> On 06/04/18 16:50, Ard Biesheuvel wrote:
>>> KVM on ARM refuses to decode load/store instructions used to perform
>>> I/O to emulated devices, and instead relies on the exception syndrome
>>> information to describe the operand register, access size, etc.
>>> This is only possible for instructions that have a single input/output
>>> register (as opposed to ones that increment the offset register, or
>>> load/store pair instructions, etc). Otherwise, QEMU crashes with the
>>> following error
>>>
>>> error: kvm run failed Function not implemented
>>> R00=01010101 R01=0008 R02=0048 R03=08000820
>>> R04=0120 R05=7faaa0e0 R06=7faaa0dc R07=7faaa0e8
>>> R08=7faaa0ec R09=7faaa088 R10=00ff R11=0080
>>> R12=ff00 R13=7fccfe08 R14=7faa835f R15=7faa887c
>>> PSR=81f3 N--- T svc32
>>> QEMU: Terminated
>>>
>>> and KVM produces a warning such as the following in the kernel log
>>>
>>> kvm [17646]: load/store instruction decoding not implemented
>>>
>>> GCC with LTO enabled will emit such instructions for Mmio[Read|Write]
>>> invocations performed in a loop, so we need to disable LTO for the
>>> IoLib library to ensure that the emitted instructions are suitable for
>>> emulated I/O under KVM
>>>
>>> Contributed-under: TianoCore Contribution Agreement 1.1
>>> Signed-off-by: Ard Biesheuvel
>>> ---
>>> ArmVirtPkg/ArmVirtQemu.dsc | 18 ++
>>> 1 file changed, 18 insertions(+)
>>>
>>> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
>>> index d74feb709cd1..e6e3d82d6ca9 100644
>>> --- a/ArmVirtPkg/ArmVirtQemu.dsc
>>> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
>>> @@ -414,3 +414,21 @@ [Components.AARCH64]
>>>
>>>NULL|ArmVirtPkg/Library/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf
>>>}
>>> +
>>> +[Components.ARM]
>>> + MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsic.inf {
>>> +
>>> + //
>>> + // KVM on ARM refuses to decode load/store instructions used to
>>> perform
>>> + // I/O to emulated devices, and instead relies on the exception
>>> syndrome
>>> + // information to describe the operand register, access size, etc.
>>> + // This is only possible for instructions that have a single
>>> input/output
>>> + // register (as opposed to ones that increment the offset register,
>>> or
>>> + // load/store pair instructions, etc).
>>> + // GCC with LTO enabled will emit such instructions for
>>> Mmio[Read|Write]
>>> + // invocations performed in a loop, so we need to disable LTO for
>>> this
>>> + // library to ensure that the emitted instructions are suitable for
>>> + // emulated I/O under KVM
>>> + //
>>> + GCC:*_GCC5_ARM_CC_FLAGS = -fno-lto
>>> + }
>>>
>>
>> Heh :) See .
>>
>> - Is there perhaps a finer-grained GCC option for this? (This is a
>> rhetorical question; I know you must have checked.)
>>
>
> Unfortunately not. That is why this is a workaround rather than a fix.
>
>> - Is this only with gcc-8?
>>
>
> I don't think so. Any GCC/GNU-ld combo that supports LTO is
> susceptible to this afaik. Even worse, I don't think this is limited
> to 32-bit ARM either, even if we've never managed to hit it.
>
>> - Should we do the same for the ArmVirtXen and ArmVirtQemuKernel
>> platforms? In turn, patch "ArmVirt.dsc.inc" instead? (BTW I have no clue
>> about Xen's emulation of the instructions at hand.)
>>
>
> This is a fix I would like to apply with moderation, so that we get a
> feeling for which platforms need it and which don't.
>
> ArmVirtQemuKernel is primarily used in TCG mode, as far as I am aware,
> by the OP-TEE guys for instance, who use secure world emulation.
>
> Xen doesn't really use I/O emulation on ARM (everything is
> paravirtualized) so I don't think it is affected.
Can you please work some of the above answers (as you see fit) into the
commit message, when you push the patch?
Reviewed-by: Laszlo Ersek
Thanks!
Laszlo
>> In general, I'm fine with the patch. According to [1] [2], this appears
>> to be the right syntax for the goal.
>>
>
> Thanks,
>
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Re: [edk2] [PATCH] ArmVirtPkg/ArmVirtQemu ARM: work around KVM limitations in LTO build
On 4 June 2018 at 17:18, Laszlo Ersek wrote:
> On 06/04/18 16:50, Ard Biesheuvel wrote:
>> KVM on ARM refuses to decode load/store instructions used to perform
>> I/O to emulated devices, and instead relies on the exception syndrome
>> information to describe the operand register, access size, etc.
>> This is only possible for instructions that have a single input/output
>> register (as opposed to ones that increment the offset register, or
>> load/store pair instructions, etc). Otherwise, QEMU crashes with the
>> following error
>>
>> error: kvm run failed Function not implemented
>> R00=01010101 R01=0008 R02=0048 R03=08000820
>> R04=0120 R05=7faaa0e0 R06=7faaa0dc R07=7faaa0e8
>> R08=7faaa0ec R09=7faaa088 R10=00ff R11=0080
>> R12=ff00 R13=7fccfe08 R14=7faa835f R15=7faa887c
>> PSR=81f3 N--- T svc32
>> QEMU: Terminated
>>
>> and KVM produces a warning such as the following in the kernel log
>>
>> kvm [17646]: load/store instruction decoding not implemented
>>
>> GCC with LTO enabled will emit such instructions for Mmio[Read|Write]
>> invocations performed in a loop, so we need to disable LTO for the
>> IoLib library to ensure that the emitted instructions are suitable for
>> emulated I/O under KVM
>>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Ard Biesheuvel
>> ---
>> ArmVirtPkg/ArmVirtQemu.dsc | 18 ++
>> 1 file changed, 18 insertions(+)
>>
>> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
>> index d74feb709cd1..e6e3d82d6ca9 100644
>> --- a/ArmVirtPkg/ArmVirtQemu.dsc
>> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
>> @@ -414,3 +414,21 @@ [Components.AARCH64]
>>
>>NULL|ArmVirtPkg/Library/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf
>>}
>> +
>> +[Components.ARM]
>> + MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsic.inf {
>> +
>> + //
>> + // KVM on ARM refuses to decode load/store instructions used to
>> perform
>> + // I/O to emulated devices, and instead relies on the exception
>> syndrome
>> + // information to describe the operand register, access size, etc.
>> + // This is only possible for instructions that have a single
>> input/output
>> + // register (as opposed to ones that increment the offset register, or
>> + // load/store pair instructions, etc).
>> + // GCC with LTO enabled will emit such instructions for
>> Mmio[Read|Write]
>> + // invocations performed in a loop, so we need to disable LTO for this
>> + // library to ensure that the emitted instructions are suitable for
>> + // emulated I/O under KVM
>> + //
>> + GCC:*_GCC5_ARM_CC_FLAGS = -fno-lto
>> + }
>>
>
> Heh :) See .
>
> - Is there perhaps a finer-grained GCC option for this? (This is a
> rhetorical question; I know you must have checked.)
>
Unfortunately not. That is why this is a workaround rather than a fix.
> - Is this only with gcc-8?
>
I don't think so. Any GCC/GNU-ld combo that supports LTO is
susceptible to this afaik. Even worse, I don't think this is limited
to 32-bit ARM either, even if we've never managed to hit it.
> - Should we do the same for the ArmVirtXen and ArmVirtQemuKernel
> platforms? In turn, patch "ArmVirt.dsc.inc" instead? (BTW I have no clue
> about Xen's emulation of the instructions at hand.)
>
This is a fix I would like to apply with moderation, so that we get a
feeling for which platforms need it and which don't.
ArmVirtQemuKernel is primarily used in TCG mode, as far as I am aware,
by the OP-TEE guys for instance, who use secure world emulation.
Xen doesn't really use I/O emulation on ARM (everything is
paravirtualized) so I don't think it is affected.
> In general, I'm fine with the patch. According to [1] [2], this appears
> to be the right syntax for the goal.
>
Thanks,
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Re: [edk2] [PATCH] ArmVirtPkg/ArmVirtQemu ARM: work around KVM limitations in LTO build
On 06/04/18 16:50, Ard Biesheuvel wrote:
> KVM on ARM refuses to decode load/store instructions used to perform
> I/O to emulated devices, and instead relies on the exception syndrome
> information to describe the operand register, access size, etc.
> This is only possible for instructions that have a single input/output
> register (as opposed to ones that increment the offset register, or
> load/store pair instructions, etc). Otherwise, QEMU crashes with the
> following error
>
> error: kvm run failed Function not implemented
> R00=01010101 R01=0008 R02=0048 R03=08000820
> R04=0120 R05=7faaa0e0 R06=7faaa0dc R07=7faaa0e8
> R08=7faaa0ec R09=7faaa088 R10=00ff R11=0080
> R12=ff00 R13=7fccfe08 R14=7faa835f R15=7faa887c
> PSR=81f3 N--- T svc32
> QEMU: Terminated
>
> and KVM produces a warning such as the following in the kernel log
>
> kvm [17646]: load/store instruction decoding not implemented
>
> GCC with LTO enabled will emit such instructions for Mmio[Read|Write]
> invocations performed in a loop, so we need to disable LTO for the
> IoLib library to ensure that the emitted instructions are suitable for
> emulated I/O under KVM
>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel
> ---
> ArmVirtPkg/ArmVirtQemu.dsc | 18 ++
> 1 file changed, 18 insertions(+)
>
> diff --git a/ArmVirtPkg/ArmVirtQemu.dsc b/ArmVirtPkg/ArmVirtQemu.dsc
> index d74feb709cd1..e6e3d82d6ca9 100644
> --- a/ArmVirtPkg/ArmVirtQemu.dsc
> +++ b/ArmVirtPkg/ArmVirtQemu.dsc
> @@ -414,3 +414,21 @@ [Components.AARCH64]
>
>NULL|ArmVirtPkg/Library/FdtPciPcdProducerLib/FdtPciPcdProducerLib.inf
>}
> +
> +[Components.ARM]
> + MdePkg/Library/BaseIoLibIntrinsic/BaseIoLibIntrinsic.inf {
> +
> + //
> + // KVM on ARM refuses to decode load/store instructions used to perform
> + // I/O to emulated devices, and instead relies on the exception
> syndrome
> + // information to describe the operand register, access size, etc.
> + // This is only possible for instructions that have a single
> input/output
> + // register (as opposed to ones that increment the offset register, or
> + // load/store pair instructions, etc).
> + // GCC with LTO enabled will emit such instructions for
> Mmio[Read|Write]
> + // invocations performed in a loop, so we need to disable LTO for this
> + // library to ensure that the emitted instructions are suitable for
> + // emulated I/O under KVM
> + //
> + GCC:*_GCC5_ARM_CC_FLAGS = -fno-lto
> + }
>
Heh :) See .
- Is there perhaps a finer-grained GCC option for this? (This is a
rhetorical question; I know you must have checked.)
- Is this only with gcc-8?
- Should we do the same for the ArmVirtXen and ArmVirtQemuKernel
platforms? In turn, patch "ArmVirt.dsc.inc" instead? (BTW I have no clue
about Xen's emulation of the instructions at hand.)
In general, I'm fine with the patch. According to [1] [2], this appears
to be the right syntax for the goal.
Thanks!
Laszlo
[1]
https://edk2-docs.gitbooks.io/edk-ii-dsc-specification/content/2_dsc_overview/24_[buildoptions]_section.html#table-8-edk-ii-buildoptions-variable-descriptions
[2]
https://edk2-docs.gitbooks.io/edk-ii-dsc-specification/content/2_dsc_overview/211_[components]_section_processing.html#211-components-section-processing
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