On Wed, Mar 29, 2017 at 05:37:49PM +0200, Laszlo Ersek wrote: > On 03/29/17 16:48, Christoffer Dall wrote: > > On Wed, Mar 29, 2017 at 10:36:51PM +0800, gengdongjiu wrote: > >> 2017-03-29 18:36 GMT+08:00, Achin Gupta <achin.gupta@xxxxxxx>: > > >>> 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. > >> > >> Sorry, As I understand it, after Qemu generate the CPER table, it > >> should pass the CPER table to the guest UEFI, then Guest UEFI place > >> this CPER table to the guest OS memory. In this flow, the Guest UEFI > >> should be involved, else the Guest OS can not see the CPER table. > >> > > > > I think you need to explain the "pass the CPER table to the guest UEFI" > > concept in terms of what really happens, step by step, and when you say > > "then Guest UEFI place the CPER table to the guest OS memory", I'm > > curious who is running what code on the hardware when doing that. > > I strongly suggest to keep the guest firmware's runtime involvement to > zero. Two reasons: > > (1) As you explained above (... which I conveniently snipped), when you > inject an interrupt to the guest, the handler registered for that > interrupt will come from the guest kernel. > > The only exception to this is when the platform provides a type of > interrupt whose handler can be registered and then locked down by the > firmware. On x86, this is the SMI. > > In practice though, > - in OVMF (x86), we only do synchronous (software-initiated) SMIs (for > privileged UEFI varstore access), > - and in ArmVirtQemu (ARM / aarch64), none of the management mode stuff > exists at all. > > I understand that the Platform Init 1.5 (or 1.6?) spec abstracted away > the MM (management mode) protocols from Intel SMM, but at this point > there is zero code in ArmVirtQemu for that. (And I'm unsure how much of > any eligible underlying hw emulation exists in QEMU.) > > So you can't get the guest firmware to react to the injected interrupt > without the guest OS coming between first. > > (2) Achin's description matches really-really closely what is possible, > and what should be done with QEMU, ArmVirtQemu, and the guest kernel. > > In any solution for this feature, the firmware has to reserve some > memory from the OS at boot. The current facilities we have enable this. > As I described previously, the ACPI linker/loader actions can be mapped > more or less 1:1 to Achin's design. From a practical perspective, you > really want to keep the guest firmware as dumb as possible (meaning: as > generic as possible), and keep the ACPI specifics to the QEMU and the > guest kernel sides. > > The error serialization actions -- the co-operation between guest kernel > and QEMU on the special memory areas -- that were mentioned earlier by > Michael and Punit look like a complication. But, IMO, they don't differ > from any other device emulation -- DMA actions in particular -- that > QEMU already does. Device models are what QEMU *does*. Read the command > block that the guest driver placed in guest memory, parse it, sanity > check it, verify it, execute it, write back the status code, inject an > interrupt (and/or let any polling guest driver notice it "soon after" -- > use barriers as necessary). > > Thus, I suggest to rely on the generic ACPI linker/loader interface > (between QEMU and guest firmware) *only* to make the firmware lay out > stuff (= reserve buffers, set up pointers, install QEMU's ACPI tables) > *at boot*. Then, at runtime, let the guest kernel and QEMU (the "device > model") talk to each other directly. Keep runtime firmware involvement > to zero. > > You *really* don't want to debug three components at runtime, when you > can solve the thing with two. (Two components whose build systems won't > drive you mad, I should add.) > > IMO, Achin's design nailed it. We can do that. > I completely agree. My questions were intended for gengdongjiu to clarify his/her position and clear up any misunderstandings between what Achin suggested and what he/she wrote. Thanks, -Christoffer
