page fault handle Post: 302356849

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Operating Systems Linux page fault handle Post 302356849 by a2156z on Monday 28th of September 2009 04:52:05 AM

09-28-2009

a2156z

Guest

page fault handle

For zero-copy communication among the processor, I allocated a pool in the kernel. From user space, it may mmap the virtual memory device into user space i.e 0x80000000. the client may send a message to the server, it may request a buffer, kernel will allocate a block for it and register it into the pool. After that, the client(user space) will got an address(that has been translated into user space address) for example: it will be 0x80003ffe4, the kernel will record the offset 0x3ffe4 into pool. But during write the the user space address 0x80003ffe4, I track the memory fault handle process, I got the vmf->virtual_address - vma->start = 0x3f000, I follow the offset 0x3f000 to find the page, in fact, the offset is not right.
So, why is the offset 0x3f000 other than 0x3ffe4?

The call flow:

char *buf = ipczalloc(6); // buf = 0x80003ffe4.
memcpy(buf, "12345", 5); // will enter vma fault handle

The code as below:
static int ipcmem_vm_nopage(struct vm_area_struct* vma, struct vm_fault * vmf)
{
unsigned long offset;
offset = vmf->virtual_address - vma->start;
printk("the offset is %x.\n", offset);
}

---------- Post updated 09-28-09 at 12:52 AM ---------- Previous update was 09-27-09 at 11:23 PM ----------

I got the answer, since the kernel before do the page fault,
the vmf.virtual_address = (void __user *)(address & PAGE_MASK)

PAGE_MASK = ~(0xFFF)

From the kernel source code, there is no way to get the real user address from vm fault handler.

So, are there any better to handle that?

a2156z

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LEARN ABOUT SUNOS

csx_put64

csx_Put8(9F)						   Kernel Functions for Drivers 					      csx_Put8(9F)

NAME

       csx_Put8, csx_Put16, csx_Put32, csx_Put64 - write to device register

SYNOPSIS

       #include <sys/pccard.h>

       void csx_Put8(acc_handle_t handle, uint32_t offset, uint8_t value);

       void csx_Put16(acc_handle_t handle, uint32_t offset, uint16_t value);

       void csx_Put32(acc_handle_t handle, uint32_t offset, uint32_t value);

       void csx_Put64(acc_handle_t handle, uint32_t offset, uint64_t value);

INTERFACE LEVEL

       Solaris DDI Specific (Solaris DDI)

PARAMETERS

       handle	       The access handle returned from csx_RequestIO(9F), csx_RequestWindow(9F), or csx_DupHandle(9F).

       offset	       The offset in bytes from the base of the mapped resource.

       value	       The data to be written to the device.

DESCRIPTION

       These functions generate a write of various sizes to the mapped memory or device register.

       The  csx_Put8(),  csx_Put16(), csx_Put32(), and csx_Put64() functions write 8 bits, 16 bits, 32 bits, and 64 bits of data, respectively, to
       the device address represented by the handle, handle, at an offset in bytes represented by the offset, offset.

       Data that consists of more than one byte will automatically be translated to maintain a consistent view between the  host  and  the  device
       based  on  the  encoded	information  in the data access handle.  The translation may involve byte swapping if the host and the device have
       incompatible endian characteristics.

CONTEXT

       These functions may be called from user, kernel, or interrupt context.

SEE ALSO

       csx_DupHandle(9F), csx_Get8(9F), csx_GetMappedAddr(9F), csx_RepGet8(9F), csx_RepPut8(9F), csx_RequestIO(9F), csx_RequestWindow(9F)

       PC Card 95 Standard, PCMCIA/JEIDA

SunOS 5.10							    19 Jul 1996 						      csx_Put8(9F)