Re: [PATCH v8 06/13] acpi/ghes: add support for generic error injection via QAPI

[Jonathan Cameron]

On Wed, 11 Sep 2024 15:21:32 +0200
Igor Mammedov <imammedo@xxxxxxxxxx> wrote:

> On Sun, 25 Aug 2024 05:29:23 +0200
> Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx> wrote:
> 
> > Em Mon, 19 Aug 2024 14:51:36 +0200
> > Igor Mammedov <imammedo@xxxxxxxxxx> escreveu:
> >   
> > > > +        read_ack = 1;
> > > > +        cpu_physical_memory_write(read_ack_start_addr,
> > > > +                                  &read_ack, (uint64_t));      
> > > we don't do this for SEV so, why are you setting it to 1 here?    
> > 
> > According with:
> > https://uefi.org/specs/ACPI/6.5/18_Platform_Error_Interfaces.html#generic-hardware-error-source-version-2-ghesv2-type-10
> > 
> >    "These are the steps the OS must take once detecting an error from a particular GHESv2 error source:
> > 
> >     OSPM detects error (via interrupt/exception or polling the block status)
> > 
> >     OSPM copies the error status block
> > 
> >     OSPM clears the block status field of the error status block
> > 
> >     OSPM acknowledges the error via Read Ack register. For example:
> > 
> >         OSPM reads the Read Ack register –> X
> > 
> >         OSPM writes –> (( X & ReadAckPreserve) | ReadAckWrite)"
> > 
> > 
> > So, basically the guest OS takes some time to detect that an error
> > is raised. When it detects, it needs to mark that the error was
> > handled.  
> 
> what you are doing here by setting read_ack = 1,
> is making ack on behalf of OSPM when OSPM haven't handled existing error yet.
> 
> Essentially making HW/FW do the job of OSPM. That looks wrong to me.
> From HW/FW side read_ack register should be thought as read-only.

It's not read-only because HW/FW has to clear it so that HW/FW can detect
when the OSPM next writes it.

Agreed this write to 1 looks wrong, but the one a few lines further down (to zero
it) is correct.

My bug a long time back I think.

Jonathan

> 
> > 
> > IMO, this is needed, independently of the notification mechanism.
> > 
> > Regards,
> > Mauro
> >   
> 
>