Re: [PATCH] kvm: pass the virtual SEI syndrome to guest OS

[gengdongjiu <gengdongjiu@huawei.com>]

Hi all/Laszlo,

  sorry, I have a question to consult with you.


On 2017/4/7 2:55, Laszlo Ersek wrote:
> On 04/06/17 14:35, gengdongjiu wrote:
>> Dear, Laszlo
>>    Thanks for your detailed explanation.
>>
>> On 2017/3/29 19:58, Laszlo Ersek wrote:
>>> (This ought to be one of the longest address lists I've ever seen :)
>>> Thanks for the CC. I'm glad Shannon is already on the CC list. For good
>>> measure, I'm adding MST and Igor.)
>>>
>>> On 03/29/17 12:36, Achin Gupta wrote:
>>>> Hi gengdongjiu,
>>>>
>>>> On Wed, Mar 29, 2017 at 05:36:37PM +0800, gengdongjiu wrote:
>>>>>
>>>>> Hi Laszlo/Biesheuvel/Qemu developer,
>>>>>
>>>>>    Now I encounter a issue and want to consult with you in ARM64 platform， as described below:
>>>>>
>>>>> when guest OS happen synchronous or asynchronous abort, kvm needs
>>>>> to send the error address to Qemu or UEFI through sigbus to
>>>>> dynamically generate APEI table. from my investigation, there are
>>>>> two ways:
>>>>>
>>>>> (1) Qemu get the error address, and generate the APEI table, then
>>>>> notify UEFI to know this generation, then inject abort error to
>>>>> guest OS, guest OS read the APEI table.
>>>>> (2) Qemu get the error address, and let UEFI to generate the APEI
>>>>> table, then inject abort error to guest OS, guest OS read the APEI
>>>>> table.
>>>>
>>>> Just being pedantic! I don't think we are talking about creating the APEI table
>>>> dynamically here. The issue is: Once KVM has received an error that is destined
>>>> for a guest it will raise a SIGBUS to Qemu. Now before Qemu can inject the error
>>>> into the guest OS, a CPER (Common Platform Error Record) has to be generated
>>>> corresponding to the error source (GHES corresponding to memory subsystem,
>>>> processor etc) to allow the guest OS to do anything meaningful with the
>>>> error. So who should create the CPER is the question.
>>>>
>>>> At the EL3/EL2 interface (Secure Firmware and OS/Hypervisor), an error arrives
>>>> at EL3 and secure firmware (at EL3 or a lower secure exception level) is
>>>> responsible for creating the CPER. ARM is experimenting with using a Standalone
>>>> MM EDK2 image in the secure world to do the CPER creation. This will avoid
>>>> adding the same code in ARM TF in EL3 (better for security). The error will then
>>>> be injected into the OS/Hypervisor (through SEA/SEI/SDEI) through ARM Trusted
>>>> Firmware.
>>>>
>>>> Qemu is essentially fulfilling the role of secure firmware at the EL2/EL1
>>>> interface (as discussed with Christoffer below). So it should generate the CPER
>>>> before injecting the error.
>>>>
>>>> This is corresponds to (1) above apart from notifying UEFI (I am assuming you
>>>> mean guest UEFI). At this time, the guest OS already knows where to pick up the
>>>> CPER from through the HEST. Qemu has to create the CPER and populate its address
>>>> at the address exported in the HEST. Guest UEFI should not be involved in this
>>>> flow. Its job was to create the HEST at boot and that has been done by this
>>>> stage.
>>>>
>>>> Qemu folk will be able to add but it looks like support for CPER generation will
>>>> need to be added to Qemu. We need to resolve this.
>>>>
>>>> Do shout if I am missing anything above.
>>>
>>> After reading this email, the use case looks *very* similar to what
>>> we've just done with VMGENID for QEMU 2.9.
>>>
>>> We have a facility between QEMU and the guest firmware, called "ACPI
>>> linker/loader", with which QEMU instructs the firmware to
>>>
>>> - allocate and download blobs into guest RAM (AcpiNVS type memory) --
>>> ALLOCATE command,
>>>
>>> - relocate pointers in those blobs, to fields in other (or the same)
>>> blobs -- ADD_POINTER command,
>>>
>>> - set ACPI table checksums -- ADD_CHECKSUM command,
>>>
>>> - and send GPAs of fields within such blobs back to QEMU --
>>> WRITE_POINTER command.
>>>
>>> This is how I imagine we can map the facility to the current use case
>>> (note that this is the first time I read about HEST / GHES / CPER):

Laszlo lists a Qemu GHES table generation solution, Mainly use the four commands: "ALLOCATE/ADD_POINTER/ADD_CHECKSUM/WRITE_POINTER" to communicate with BIOS
so whether the four commands needs to be supported by the guest firware/UEFI.  I found the  "WRITE_POINTER" always failed. so I suspect guest UEFI/firmware not support the "WRITE_POINTER" command. please help me confirm it, thanks so much.