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[Qemu-devel] RFC: New API for PPC for vcpu mmu access


From: Yoder Stuart-B08248
Subject: [Qemu-devel] RFC: New API for PPC for vcpu mmu access
Date: Wed, 2 Feb 2011 20:33:35 +0000

Below is a proposal for a new API for PPC to allow KVM clients
to set MMU state in a vcpu.

BookE processors have one or more software managed TLBs and
currently there is no mechanism for Qemu to initialize
or access them.  This is needed for normal initialization
as well as debug.

There are 4 APIs:
   
-KVM_PPC_SET_MMU_TYPE allows the client to negotiate the type
 of MMU with KVM-- the type determines the size and format
 of the data in the other APIs

-KVM_PPC_INVALIDATE_TLB invalidates all TLB entries in all
 TLBs in the vcpu

-KVM_PPC_SET_TLBE sets a TLB entry-- the Power architecture
 specifies the format of the MMU data passed in

-KVM_PPC_GET_TLB allows searching, reading a specific TLB entry,
 or iterating over an entire TLB.  Some TLBs may have an unspecified
 geometry and thus the need to be able to iterate in order
 to dump the TLB.  The Power architecture specifies the format
 of the MMU data

Feedback welcome.

Thanks,
Stuart Yoder

------------------------------------------------------------------

KVM PPC MMU API
---------------

User space can query whether the APIs to access the vcpu mmu
is available with the KVM_CHECK_EXTENSION API using
the KVM_CAP_PPC_MMU argument.

If the KVM_CAP_PPC_MMU return value is non-zero it specifies that
the following APIs are available:

   KVM_PPC_SET_MMU_TYPE
   KVM_PPC_INVALIDATE_TLB
   KVM_PPC_SET_TLBE
   KVM_PPC_GET_MMU


KVM_PPC_SET_MMU_TYPE
--------------------

Capability: KVM_CAP_PPC_SET_MMU_TYPE
Architectures: powerpc
Type: vcpu ioctl
Parameters: __u32 mmu_type (in)
Returns: 0 if specified MMU type is supported, else -1

Sets the MMU type.  Valid input values are:
   BOOKE_NOHV   0x1
   BOOKE_HV     0x2

A return value of 0x0 indicates that KVM supports
the specified MMU type.

KVM_PPC_INVALIDATE_TLB
----------------------

Capability: KVM_CAP_PPC_MMU
Architectures: powerpc
Type: vcpu ioctl
Parameters: none
Returns: 0 on success, -1 on error

Invalidates all TLB entries in all TLBs of the vcpu.

KVM_PPC_SET_TLBE
----------------

Capability: KVM_CAP_PPC_MMU
Architectures: powerpc
Type: vcpu ioctl
Parameters:
        For mmu types BOOKE_NOHV and BOOKE_HV : struct kvm_ppc_booke_mmu (in)
Returns: 0 on success, -1 on error

Sets an MMU entry in a virtual CPU.

For mmu types BOOKE_NOHV and BOOKE_HV:

      To write a TLB entry, set the mas fields of kvm_ppc_booke_mmu 
      as per the Power architecture.

      struct kvm_ppc_booke_mmu {
            union {
                  __u64 mas0_1;
                  struct {
                        __u32 mas0;
                        __u32 mas1;
                  };
            };
            __u64 mas2;
            union {
                  __u64 mas7_3      
                  struct {
                        __u32 mas7;
                        __u32 mas3;
                  };
            };
            union {
                  __u64 mas5_6      
                  struct {
                        __u64 mas5;
                        __u64 mas6;
                  };
            }
            __u32 mas8;
      };

      For a mmu type of BOOKE_NOHV, the mas5 and mas8 fields
      in kvm_ppc_booke_mmu are present but not supported.


KVM_PPC_GET_TLB
---------------

Capability: KVM_CAP_PPC_MMU
Architectures: powerpc
Type: vcpu ioctl
Parameters: struct kvm_ppc_get_mmu (in/out)
Returns: 0 on success
         -1 on error
         errno = ENOENT when iterating and there are no more entries to read

Reads an MMU entry from a virtual CPU.

      struct kvm_ppc_get_mmu {
            /* in */
                void *mmu;
            __u32 flags;
                  /* a bitmask of flags to the API */
                    /*     TLB_READ_FIRST   0x1      */
                    /*     TLB_SEARCH       0x2      */
            /* out */
            __u32 max_entries;
      };

For mmu types BOOKE_NOHV and BOOKE_HV :

      The "void *mmu" field of kvm_ppc_get_mmu points to 
        a struct of type "struct kvm_ppc_booke_mmu".

      If TLBnCFG[NENTRY] > 0 and TLBnCFG[ASSOC] > 0, the TLB has
      of known number of entries and associativity.  The mas0[ESEL]
      and mas2[EPN] fields specify which entry to read.
      
      If TLBnCFG[NENTRY] == 0 the number of TLB entries is 
      undefined and this API can be used to iterate over
      the entire TLB selected with TLBSEL in mas0.
      
      -To read a TLB entry:
      
         set the following fields in the mmu struct (struct kvm_ppc_booke_mmu):
            flags=0
            mas0[TLBSEL] // select which TLB is being read
            mas0[ESEL]   // select which entry is being read
            mas2[EPN]    // effective address 
      
         On return the following fields are updated as per the Power 
architecture:
            mas0
            mas1 
            mas2 
            mas3 
            mas7 
      
      -To iterate over a TLB (read all entries):
      
        To start an interation sequence, set the following fields in
        the mmu struct (struct kvm_ppc_booke_mmu)
            flags=TLB_READ_FIRST
            mas0[TLBSEL]  // select which TLB is being read
      
        On return the following fields are updated:
            mas0           // set as per Power arch
            mas1           // set as per Power arch
            mas2           // set as per Power arch
            mas3           // set as per Power arch
            mas7           // set as per Power arch
            max_entries    // Contains upper limit on number of entries that may
                           // be returned. A value of 0xffffffff means there is
                           // no meaningful upper bound.
         
        For subsequent calls to the API the following output fields must
        be passed back into the API unmodified:
            flags
            mas0
            mas2
      
        A return value of -ENOENT indicates that there are no more
        entries to be read.
      
      -To search for TLB entry
      
         To search for TLB entry, set the following fields in
         the mmu struct (struct kvm_ppc_booke_mmu):
            flags=TLB_SEARCH
            mas2[EPN]    // effective address to search for
            mas6         // set as per the Power arch
            mas5         // set as per the Power arch
      
         On return, the following fields are updated as per the Power 
architecture:
            mas0
            mas1 
            mas2 
            mas3 
            mas7 




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