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x86/hyperv: Fix unused variable 'msr_val' warning in hv_qlock_wait

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Fixes the following W=1 kernel build warning(s):
arch/x86/hyperv/hv_spinlock.c:28:16: warning: variable ‘msr_val’ set but not used [-Wunused-but-set-variable]
  unsigned long msr_val;

As Hypervisor Top-Level Functional Specification states in chapter 7.5
Virtual Processor Idle Sleep State, "A partition which possesses the
AccessGuestIdleMsr privilege (refer to section 4.2.2) may trigger entry
into the virtual processor idle sleep state through a read to the
hypervisor-defined MSR HV_X64_MSR_GUEST_IDLE".

That means only a read of the MSR is necessary. The returned value
msr_val is not used. Cast it to void to silence this warning.

Reference:
https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Xu Yihang <xuyihang@huawei.com>
Link: https://lore.kernel.org/r/20210323024302.174434-1-xuyihang@huawei.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
This commit is contained in:
Xu Yihang 2021-03-23 10:43:02 +08:00 committed by Wei Liu
parent 6bbdc3db76
commit 13c4d4626a
1 changed files with 6 additions and 2 deletions
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8
arch/x86/hyperv/hv_spinlock.c
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@ -25,7 +25,6 @@ static void hv_qlock_kick(int cpu)
static void hv_qlock_wait(u8 *byte, u8 val)
{
unsigned long msr_val;
unsigned long flags;
if (in_nmi())
@ -48,8 +47,13 @@ static void hv_qlock_wait(u8 *byte, u8 val)
/*
* Only issue the rdmsrl() when the lock state has not changed.
*/
if (READ_ONCE(*byte) == val)
if (READ_ONCE(*byte) == val) {
unsigned long msr_val;
rdmsrl(HV_X64_MSR_GUEST_IDLE, msr_val);
(void)msr_val;
}
local_irq_restore(flags);
}