Re: [Xen-devel] [PATCH RFC 3/4] x86: add invpcid.h

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 15/02/18 12:24, Wei Liu wrote:
> On Thu, Feb 15, 2018 at 12:15:56PM +0000, Andrew Cooper wrote:
>> On 15/02/18 12:10, Wei Liu wrote:
>>> Provide the functions needed for different modes.
>>>
>>> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>>> ---
>>>  xen/include/asm-x86/invpcid.h | 61 
>>> +++++++++++++++++++++++++++++++++++++++++++
>>>  1 file changed, 61 insertions(+)
>>>  create mode 100644 xen/include/asm-x86/invpcid.h
>>>
>>> diff --git a/xen/include/asm-x86/invpcid.h b/xen/include/asm-x86/invpcid.h
>>> new file mode 100644
>>> index 0000000000..7c307ecfc3
>>> --- /dev/null
>>> +++ b/xen/include/asm-x86/invpcid.h
>>> @@ -0,0 +1,61 @@
>>> +#ifndef _ASM_X86_INVPCID_H_
>>> +#define _ASM_X86_INVPCID_H_
>>> +
>>> +#include <xen/types.h>
>>> +
>>> +#define INVPCID_TYPE_INDIV_ADDR      0
>>> +#define INVPCID_TYPE_SINGLE_CTXT     1
>>> +#define INVPCID_TYPE_ALL_INCL_GLOBAL 2
>>> +#define INVPCID_TYPE_ALL_NON_GLOBAL  3
>>> +
>>> +struct invpcid_desc {
>>> +    uint64_t pcid:12;
>>> +    uint64_t reserved:52;
>>> +    uint64_t addr;
>>> +};
>>> +
>>> +static inline void invpcid(unsigned long pcid, unsigned long addr,
>>> +                           unsigned long type)
>>> +{
>>> +    struct invpcid_desc desc = { .pcid = pcid, .addr = addr };
>>> +
>>> +    asm volatile ("invpcid (%0), %1"
>>> +                  : : "r" (&desc), "r" (type) : "memory" );
>> invpcid %[desc], %[type]
>>
>> And you can use [desc] "m" (desc) for the constraint.  The structure
>> will be built on the stack, meaning that an %rsp based memory reference
>> is more efficient than forcing the use of a register.
> NP.
>
>> We probably also need a -DHAVE_GAS_INVPCID, as INVPCID is newer than
>> some of the instruction groups we already check for.
>>
> Or we can just use the byte code directly -- it is the same for both 64
> and 32 bit, then manually specify the ModRM byte. That's what Linux
> does.

See the vmx __invept() wrapper, which is very similar, but doesn't need
the BUG() handling.

~Andrew

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