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Re: [PATCH v2 11/18] KVM/MIPS32: Routines to handle specific traps/excep

To: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH v2 11/18] KVM/MIPS32: Routines to handle specific traps/exceptions while executing the guest.
From: Sanjay Lal <sanjayl@kymasys.com>
Date: Mon, 18 Feb 2013 18:31:17 -0800
Cc: kvm@vger.kernel.org, linux-mips@linux-mips.org
In-reply-to: <20130218094450.GA9817@redhat.com>
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On Feb 18, 2013, at 1:44 AM, Gleb Natapov wrote:

> On Fri, Feb 15, 2013 at 11:10:46AM -0500, Sanjay Lal wrote:
>> 
>> On Feb 6, 2013, at 8:20 AM, Gleb Natapov wrote:
>> 
>>> On Wed, Nov 21, 2012 at 06:34:09PM -0800, Sanjay Lal wrote:
>>>> +static gpa_t kvm_trap_emul_gva_to_gpa_cb(gva_t gva)
>>>> +{
>>>> +  gpa_t gpa;
>>>> +  uint32_t kseg = KSEGX(gva);
>>>> +
>>>> +  if ((kseg == CKSEG0) || (kseg == CKSEG1))
>>> You seems to be using KVM_GUEST_KSEGX variants on gva in all other
>>> places. Why not here?
>> 
>> This function is invoked to handle 2 scenarios:
>> (1) Parse the boot code config tables setup by QEMU's Malta emulation. The 
>> pointers in the tables are actual KSEG0 addresses (unmapped, cached) and not 
>> Guest KSEG0 addresses.
>> 
> Where is it called for that purpose? The only place where gva_to_gpa
> callback is called is in kvm/kvm_mips_emul.c:kvm_mips_emulate_(store|load)
Load/stores from/to KSEG1 generate the Address Error Load/Store exceptions. The 
handler calls kvm_mips_emul.c:kvm_mips_emulate_(store|load) which then call the 
gva_to_gpa callback.

> 
>> (2) Handle I/O accesses by the guest.  On MIPS platforms, I/O device 
>> registers are mapped into the KSEG1 address space (unmapped, uncached).  
>> Again like (1) these are actual KSEG1 addresses, which cause an exception 
>> and are passed onto QEMU for I/O emulation.
>> 
> So guest KSEG1 registers is mapped to 0xA0000000-0xBFFFFFFF ranges just
> like on a host? Can you give corresponding segment names to those ranges
> 
> Guest User address space:   0x00000000 -> 0x40000000 (useg?)
> Guest Kernel Unmapped:      0x40000000 -> 0x60000000 (kseg0?)
> Guest Kernel Mapped:        0x60000000 -> 0x80000000 (?)
> 


Yes, now that you mention it :-). I'll add a corresponding Guest Kernel KSEG1 
segment name.

Regards
Sanjay



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