Re: [Xen-devel] [PATCH 1/2] x86/tboot: invalidate FIX_TBOOT_MAP_ADDRESS mapping after use

["Wei, Gang" <gang.wei@xxxxxxxxx>]

On Mar 5, 2015 15:14, Jan Beulich wrote:
>>>> On 05.03.15 at 05:45, <gang.wei@xxxxxxxxx> wrote:
>> On Feb 18, 2015 17:03, Jan Beulich wrote:
>>> In order for commit cbeeaa7d ("x86/nmi: fix shootdown of pcpus running
>>> in VMX non-root mode")'s re-use of that fixmap entry to not cause
>>> undesirable (in crash context) cross-CPU TLB flushes, invalidate the
>>> fixmap entry right after use.
>>> 
>>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>>> 
>>> --- a/xen/arch/x86/tboot.c
>>> +++ b/xen/arch/x86/tboot.c
>>> @@ -138,6 +138,7 @@ void __init tboot_probe(void)
>>>                        TXT_PUB_CONFIG_REGS_BASE + TXTCR_SINIT_BASE);
>>>                        tboot_copy_memory((unsigned char *)&sinit_size,
>>>                        sizeof(sinit_size), TXT_PUB_CONFIG_REGS_BASE +
>>>                        TXTCR_SINIT_SIZE);
>>> +    __set_fixmap(FIX_TBOOT_MAP_ADDRESS, 0, 0);
>>>  }
>>>  
>>>  /* definitions from xen/drivers/passthrough/vtd/iommu.h
>>> @@ -476,6 +477,8 @@ int __init tboot_parse_dmar_table(acpi_t
>>>      dmar_table_raw = xmalloc_array(unsigned char, dmar_table_length);
>>>      tboot_copy_memory(dmar_table_raw, dmar_table_length, pa);
>>>      dmar_table = (struct acpi_table_header *)dmar_table_raw;
>>> +    __set_fixmap(FIX_TBOOT_MAP_ADDRESS, 0, 0);
>>> +
>>>      rc = dmar_handler(dmar_table);
>>>      xfree(dmar_table_raw);
>>> 
>> 
>> It might be better to move the fixmap invalidations into
>> tboot_copy_memory like below.
> 
> I considered this, but dropped the idea due to resulting in several
> redundant invalidations.

From performance perspective, I am ok with your final changes.

Jimmy



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