Re: [Xen-devel] [PATCH v2 for 4.5] ioreq-server: handle the lack of a default emulator properly

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.09.14 at 12:59, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 29/09/14 11:21, Paul Durrant wrote:
>> I started porting QEMU over to use the new ioreq server API and hit a
>> problem with PCI bus enumeration. Because, with my patches, QEMU only
>> registers to handle config space accesses for the PCI device it implements
>> all other attempts by the guest to access 0xcfc go nowhere and this was
>> causing the vcpu to wedge up because nothing was completing the I/O.
>>
>> This patch introduces an I/O completion handler into the hypervisor for the
>> case where no ioreq server matches a particular request. Read requests are
>> completed with 0xf's in the data buffer, writes and all other I/O req types
>> are ignored.
>>
>> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
>> Cc: Keir Fraser <keir@xxxxxxx>
>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>> ---
>> v2: - First non-RFC submission
>>     - Removed warning on unemulated MMIO accesses
>>
>>  xen/arch/x86/hvm/hvm.c |   35 ++++++++++++++++++++++++++++++++---
>>  1 file changed, 32 insertions(+), 3 deletions(-)
>>
>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
>> index 5c7e0a4..822ac37 100644
>> --- a/xen/arch/x86/hvm/hvm.c
>> +++ b/xen/arch/x86/hvm/hvm.c
>> @@ -2386,8 +2386,7 @@ static struct hvm_ioreq_server 
> *hvm_select_ioreq_server(struct domain *d,
>>      if ( list_empty(&d->arch.hvm_domain.ioreq_server.list) )
>>          return NULL;
>>  
>> -    if ( list_is_singular(&d->arch.hvm_domain.ioreq_server.list) ||
>> -         (p->type != IOREQ_TYPE_COPY && p->type != IOREQ_TYPE_PIO) )
>> +    if ( p->type != IOREQ_TYPE_COPY && p->type != IOREQ_TYPE_PIO )
>>          return d->arch.hvm_domain.default_ioreq_server;
>>  
>>      cf8 = d->arch.hvm_domain.pci_cf8;
>> @@ -2618,12 +2617,42 @@ bool_t hvm_send_assist_req_to_ioreq_server(struct 
> hvm_ioreq_server *s,
>>      return 0;
>>  }
>>  
>> +static bool_t hvm_complete_assist_req(ioreq_t *p)
>> +{
>> +    switch (p->type)
>> +    {
>> +    case IOREQ_TYPE_COPY:
>> +    case IOREQ_TYPE_PIO:
>> +        if ( p->dir == IOREQ_READ )
>> +        {
>> +            if ( !p->data_is_ptr )
>> +                p->data = ~0ul;
>> +            else
>> +            {
>> +                int i, sign = p->df ? -1 : 1;
>> +                uint32_t data = ~0;
>> +
>> +                for ( i = 0; i < p->count; i++ )
>> +                    hvm_copy_to_guest_phys(p->data + sign * i * p->size, 
>> &data,
>> +                                           p->size);
> 
> This is surely bogus for an `ins` which crosses a page boundary?

Crossing page boundaries gets dealt with up the call stack in
hvmemul_linear_to_phys(), namely the path exiting with
X86EMUL_UNHANDLEABLE when done == 0.

Jan


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