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Quentin forwards a report from Hyesoo Yu, describing an interesting
problem with the use of WFxT in __delay() when a vcpu is loaded and
that KVM is *not* in VHE mode (either nVHE or hVHE).
In this case, CNTVOFF_EL2 is set to a non-zero value to reflect the
state of the guest virtual counter. At the same time, __delay() is
using get_cycles() to read the counter value, which is indirected to
reading CNTPCT_EL0.
The core of the issue is that WFxT is using the *virtual* counter,
while the kernel is using the physical counter, and that the offset
introduces a really bad discrepancy between the two.
Fix this by forcing the use of CNTVCT_EL0, making __delay() consistent
irrespective of the value of CNTVOFF_EL2.
Reported-by: Hyesoo Yu <hyesoo.yu@samsung.com>
Reported-by: Quentin Perret <qperret@google.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Fixes:
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| .. | ||
| .gitignore | ||
| clear_page.S | ||
| clear_user.S | ||
| copy_from_user.S | ||
| copy_page.S | ||
| copy_template.S | ||
| copy_to_user.S | ||
| csum.c | ||
| delay.c | ||
| error-inject.c | ||
| insn.c | ||
| kasan_sw_tags.S | ||
| Makefile | ||
| memchr.S | ||
| memcmp.S | ||
| memcpy.S | ||
| memset.S | ||
| mte.S | ||
| strchr.S | ||
| strcmp.S | ||
| strlen.S | ||
| strncmp.S | ||
| strnlen.S | ||
| strrchr.S | ||
| tishift.S | ||
| uaccess_flushcache.c | ||
| xor-neon.c | ||