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x86/entry: Optimize local_db_save() for virt 

Because DRn access is 'difficult' with virt; but the DR7 read is cheaper
than a cacheline miss on native, add a virt specific fast path to
local_db_save(), such that when breakpoints are not in use to avoid
touching DRn entirely.

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20200529213321.187833200@infradead.org
This commit is contained in:
Peter Zijlstra 2020-05-29 23:27:36 +02:00 committed by Thomas Gleixner
parent cd840e424f
commit 84b6a34915
3 changed files with 27 additions and 6 deletions
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5
arch/x86/include/asm/debugreg.h
View File

@ -85,7 +85,7 @@ static inline void hw_breakpoint_disable(void)
set_debugreg(0UL, 3);
}
static inline int hw_breakpoint_active(void)
static inline bool hw_breakpoint_active(void)
{
return __this_cpu_read(cpu_dr7) & DR_GLOBAL_ENABLE_MASK;
}
@ -117,6 +117,9 @@ static __always_inline unsigned long local_db_save(void)
{
unsigned long dr7;
if (static_cpu_has(X86_FEATURE_HYPERVISOR) && !hw_breakpoint_active())
return 0;
get_debugreg(dr7, 7);
dr7 &= ~0x400; /* architecturally set bit */
if (dr7)

26
arch/x86/kernel/hw_breakpoint.c
View File

@ -99,6 +99,8 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
unsigned long *dr7;
int i;
lockdep_assert_irqs_disabled();
for (i = 0; i < HBP_NUM; i++) {
struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
@ -117,6 +119,12 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
dr7 = this_cpu_ptr(&cpu_dr7);
*dr7 |= encode_dr7(i, info->len, info->type);
/*
* Ensure we first write cpu_dr7 before we set the DR7 register.
* This ensures an NMI never see cpu_dr7 0 when DR7 is not.
*/
barrier();
set_debugreg(*dr7, 7);
if (info->mask)
set_dr_addr_mask(info->mask, i);
@ -136,9 +144,11 @@ int arch_install_hw_breakpoint(struct perf_event *bp)
void arch_uninstall_hw_breakpoint(struct perf_event *bp)
{
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
unsigned long *dr7;
unsigned long dr7;
int i;
lockdep_assert_irqs_disabled();
for (i = 0; i < HBP_NUM; i++) {
struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
@ -151,12 +161,20 @@ void arch_uninstall_hw_breakpoint(struct perf_event *bp)
if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
return;
dr7 = this_cpu_ptr(&cpu_dr7);
*dr7 &= ~__encode_dr7(i, info->len, info->type);
dr7 = this_cpu_read(cpu_dr7);
dr7 &= ~__encode_dr7(i, info->len, info->type);
set_debugreg(*dr7, 7);
set_debugreg(dr7, 7);
if (info->mask)
set_dr_addr_mask(0, i);
/*
* Ensure the write to cpu_dr7 is after we've set the DR7 register.
* This ensures an NMI never see cpu_dr7 0 when DR7 is not.
*/
barrier();
this_cpu_write(cpu_dr7, dr7);
}
static int arch_bp_generic_len(int x86_len)

2
arch/x86/kvm/vmx/nested.c
View File

@ -3087,9 +3087,9 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
/*
* VMExit clears RFLAGS.IF and DR7, even on a consistency check.
*/
local_irq_enable();
if (hw_breakpoint_active())
set_debugreg(__this_cpu_read(cpu_dr7), 7);
local_irq_enable();
preempt_enable();
/*