Re: [Xen-devel] [PATCH v5 6/9] ioreq-server: add support for multiple servers

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.05.14 at 16:12, <Paul.Durrant@xxxxxxxxxx> wrote:
>>  -----Original Message-----
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: 07 May 2014 15:08
>> To: Paul Durrant
>> Cc: Ian Campbell; Ian Jackson; Stefano Stabellini; xen-devel@xxxxxxxxxxxxx 
>> Subject: RE: [PATCH v5 6/9] ioreq-server: add support for multiple servers
>> 
>> >>> On 07.05.14 at 14:37, <Paul.Durrant@xxxxxxxxxx> wrote:
>> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >> >>> On 07.05.14 at 14:25, <Paul.Durrant@xxxxxxxxxx> wrote:
>> >> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >> >> >>> On 07.05.14 at 14:06, <Paul.Durrant@xxxxxxxxxx> wrote:
>> >> >> >> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> >> >> >> >>> On 01.05.14 at 14:08, <paul.durrant@xxxxxxxxxx> wrote:
>> >> >> >> > +static int hvm_access_cfc(
>> >> >> >> > +    int dir, uint32_t port, uint32_t bytes, uint32_t *val)
>> >> >> >> > +{
>> >> >> >> > +    struct vcpu *curr = current;
>> >> >> >> > +    struct hvm_domain *hd = &curr->domain->arch.hvm_domain;
>> >> >> >> > +    int rc;
>> >> >> >> > +
>> >> >> >> > +    BUG_ON(port < 0xcfc);
>> >> >> >> > +    port -= 0xcfc;
>> >> >> >> > +
>> >> >> >> > +    spin_lock(&hd->pci_lock);
>> >> >> >> > +
>> >> >> >> > +    if ( hd->pci_cf8 & (1 << 31) ) {
>> >> >> >> > +        /* Fall through to an emulator */
>> >> >> >> > +        rc = X86EMUL_UNHANDLEABLE;
>> >> >> >> > +    } else {
>> >> >> >> > +        /* Config access disabled */
>> >> >> >>
>> >> >> >> Why does this not also get passed through to an emulator?
>> >> >> >>
>> >> >> >
>> >> >> > I was trying to be consistent with QEMU here. It squashes any data
>> >> >> accesses
>> >> >> > if cf8 has the top bit set.
>> >> >>
>> >> >> But afaict with that dropped the entire function can go away.
>> >> >>
>> >> >
>> >> > Yes, it can. Do you not think it would be a good idea to be consistent
>> with
>> >> > QEMU though?
>> >>
>> >> By removing the function you're going to be consistent with qemu,
>> >> because you're going to have qemu supply the data.
>> >>
>> >
>> > Yes, true, in select_ioreq_server() I could just pass cfc accesses to the
>> > default emulator if cf8 has the top bit set.
>> 
>> I continue to fail to see why you make this dependent on the value
>> of the top bit - just have any accesses to port 0xCFC be handled by
>> the emulator responsible for the respective device.
> 
> Because, according to what I read, unless cf8 has the top bit set, a 
> subsequent access to cfc should not be treated as a config cycle.

Oh, right, I mis-read your previous comment.

Jan


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