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hv:remove accessing shared log buffer cases between stac/clac

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Shared buffer is allocated by VM and is protected by SMAP.
Accessing to shared buffer between stac/clac pair will invalidate
SMAP protection.This patch is to remove these cases.
Fix minor stac/clac mis-usage,and add comments as stac/clac usage BKM

Tracked-On: #2526
Signed-off-by: Yonghua Huang <yonghua.huang@intel.com>
Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>
This commit is contained in:
Yonghua Huang
2019-04-30 21:28:36 +08:00
committed by wenlingz
parent 321ad5c374
commit be2fe2a44d
5 changed files with 17 additions and 9 deletions
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15
hypervisor/include/arch/x86/cpu.h
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@@ -464,6 +464,21 @@ static inline void write_xcr(int32_t reg, uint64_t val)
asm volatile("xsetbv" : : "c" (reg), "a" ((uint32_t)val), "d" ((uint32_t)(val >> 32U)));
}
/*
* stac/clac pair is used to access guest's memory protected by SMAP,
* following below flow:
*
* stac();
* #access guest's memory.
* clac();
*
* Notes:Avoid inserting another stac/clac pair between stac and clac,
* As once clac after multiple stac will invalidate SMAP protection
* and hence Page Fault crash.
* Logging message to memory buffer will induce this case,
* please disable SMAP temporlly or don't log messages to shared
* memory buffer, if it is evitable for you for debug purpose.
*/
static inline void stac(void)
{
asm volatile ("stac" : : : "memory");