[PATCH v4 08/10] x86/hyper-v: use hypercall for remote TLB flush

Vitaly Kuznetsov
2017-05-24T12:04:53Z

Hyper-V host can suggest us to use hypercall for doing remote TLB flush,
this is supposed to work faster than IPIs.

Implementation details: to do HvFlushVirtualAddress{Space,List} hypercalls
we need to put the input somewhere in memory and we don't really want to
have memory allocation on each call so we pre-allocate per cpu memory areas
on boot. These areas are of fixes size, limit them with an arbitrary number
of 16 (16 gvas are able to specify 16 * 4096 pages).

pv_ops patching is happening very early so we need to separate
hyperv_setup_mmu_ops() and hyper_alloc_mmu().

It is possible and easy to implement local TLB flushing too and there is
even a hint for that. However, I don't see a room for optimization on the
host side as both hypercall and native tlb flush will result in vmexit. The
hint is also not set on modern Hyper-V versions.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Acked-by: K. Y. Srinivasan <kys@microsoft.com>
Tested-by: Simon Xiao <sixiao@microsoft.com>
Tested-by: Srikanth Myakam <v-srm@microsoft.com>
---
arch/x86/hyperv/Makefile | 2 +-
arch/x86/hyperv/hv_init.c | 2 +
arch/x86/hyperv/mmu.c | 117 +++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/mshyperv.h | 3 +
arch/x86/include/uapi/asm/hyperv.h | 7 +++
arch/x86/kernel/cpu/mshyperv.c | 1 +
6 files changed, 131 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/hyperv/mmu.c

diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
index 171ae09..367a820 100644
--- a/arch/x86/hyperv/Makefile
+++ b/arch/x86/hyperv/Makefile
@@ -1 +1 @@
-obj-y := hv_init.o
+obj-y := hv_init.o mmu.o
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 7fd9cd3..df3252f 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -140,6 +140,8 @@ void hyperv_init(void)
hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);

+ hyper_alloc_mmu();
+
/*
* Register Hyper-V specific clocksource.
*/
diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
new file mode 100644
index 0000000..e3ab9b9
--- /dev/null
+++ b/arch/x86/hyperv/mmu.c
@@ -0,0 +1,117 @@
+#include <linux/types.h>
+#include <linux/hyperv.h>
+#include <linux/slab.h>
+#include <linux/log2.h>
+#include <asm/mshyperv.h>
+#include <asm/tlbflush.h>
+#include <asm/msr.h>
+#include <asm/fpu/api.h>
+
+/* HvFlushVirtualAddressSpace, HvFlushVirtualAddressList hypercalls */
+struct hv_flush_pcpu {
+ __u64 address_space;
+ __u64 flags;
+ __u64 processor_mask;
+ __u64 gva_list[];
+};
+
+static struct hv_flush_pcpu __percpu *pcpu_flush;
+
+static void hyperv_flush_tlb_others(const struct cpumask *cpus,
+ struct mm_struct *mm, unsigned long start,
+ unsigned long end)
+{
+ struct hv_flush_pcpu *flush;
+ unsigned long cur, flags;
+ u64 status = -1ULL;
+ int cpu, vcpu, gva_n, max_gvas;
+
+ if (!pcpu_flush || !hv_hypercall_pg)
+ goto do_native;
+
+ if (cpumask_empty(cpus))
+ return;
+
+ local_irq_save(flags);
+
+ flush = this_cpu_ptr(pcpu_flush);
+
+ if (mm) {
+ flush->address_space = virt_to_phys(mm->pgd);
+ flush->flags = 0;
+ } else {
+ flush->address_space = 0;
+ flush->flags = HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES;
+ }
+
+ flush->processor_mask = 0;
+ if (cpumask_equal(cpus, cpu_present_mask)) {
+ flush->flags |= HV_FLUSH_ALL_PROCESSORS;
+ } else {
+ for_each_cpu(cpu, cpus) {
+ vcpu = hv_cpu_number_to_vp_number(cpu);
+ if (vcpu != -1 && vcpu < 64)
+ flush->processor_mask |= 1 << vcpu;
+ else
+ goto do_native;
+ }
+ }
+
+ /*
+ * We can flush not more than max_gvas with one hypercall. Flush the
+ * whole address space if we were asked to do more.
+ */
+ max_gvas = (PAGE_SIZE - sizeof(*flush)) / 8;
+
+ if (end == TLB_FLUSH_ALL ||
+ (end && ((end - start)/(PAGE_SIZE*PAGE_SIZE)) > max_gvas)) {
+ if (end == TLB_FLUSH_ALL)
+ flush->flags |= HV_FLUSH_NON_GLOBAL_MAPPINGS_ONLY;
+ status = hv_do_hypercall(HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE,
+ flush, NULL);
+ } else {
+ cur = start;
+ gva_n = 0;
+ do {
+ flush->gva_list[gva_n] = cur & PAGE_MASK;
+ /*
+ * Lower 12 bits encode the number of additional
+ * pages to flush (in addition to the 'cur' page).
+ */
+ if (end >= cur + PAGE_SIZE * PAGE_SIZE)
+ flush->gva_list[gva_n] |= ~PAGE_MASK;
+ else if (end > cur)
+ flush->gva_list[gva_n] |=
+ (end - cur - 1) >> PAGE_SHIFT;
+
+ cur += PAGE_SIZE * PAGE_SIZE;
+ ++gva_n;
+
+ } while (cur < end);
+
+ status = hv_do_rep_hypercall(HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST,
+ gva_n, 0, flush, NULL);
+
+ }
+
+ local_irq_restore(flags);
+
+ if (!(status & 0xffff))
+ return;
+do_native:
+ native_flush_tlb_others(cpus, mm, start, end);
+}
+
+void hyperv_setup_mmu_ops(void)
+{
+ if (ms_hyperv.hints & HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED) {
+ pr_info("Hyper-V: Using hypercall for remote TLB flush\n");
+ pv_mmu_ops.flush_tlb_others = hyperv_flush_tlb_others;
+ }
+}
+
+void hyper_alloc_mmu(void)
+{
+ if (ms_hyperv.hints & HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED)
+ pcpu_flush = __alloc_percpu(PAGE_SIZE, PAGE_SIZE);
+}
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index cdf2391..783a8f6 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -311,6 +311,8 @@ static inline int hv_cpu_number_to_vp_number(int cpu_number)
}

void hyperv_init(void);
+void hyperv_setup_mmu_ops(void);
+void hyper_alloc_mmu(void);
void hyperv_report_panic(struct pt_regs *regs);
bool hv_is_hypercall_page_setup(void);
void hyperv_cleanup(void);
@@ -321,6 +323,7 @@ static inline bool hv_is_hypercall_page_setup(void)
return false;
}
static inline hyperv_cleanup(void) {}
+static inline void hyperv_setup_mmu_ops(void) {}
#endif /* CONFIG_HYPERV */

#ifdef CONFIG_HYPERV_TSCPAGE
diff --git a/arch/x86/include/uapi/asm/hyperv.h b/arch/x86/include/uapi/asm/hyperv.h
index c87e900..3d44036 100644
--- a/arch/x86/include/uapi/asm/hyperv.h
+++ b/arch/x86/include/uapi/asm/hyperv.h
@@ -239,6 +239,8 @@
(~((1ull << HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_SHIFT) - 1))

/* Declare the various hypercall operations. */
+#define HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE 0x0002
+#define HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST 0x0003
#define HVCALL_NOTIFY_LONG_SPIN_WAIT 0x0008
#define HVCALL_POST_MESSAGE 0x005c
#define HVCALL_SIGNAL_EVENT 0x005d
@@ -256,6 +258,11 @@
#define HV_PROCESSOR_POWER_STATE_C2 2
#define HV_PROCESSOR_POWER_STATE_C3 3

+#define HV_FLUSH_ALL_PROCESSORS 0x00000001
+#define HV_FLUSH_ALL_VIRTUAL_ADDRESS_SPACES 0x00000002
+#define HV_FLUSH_NON_GLOBAL_MAPPINGS_ONLY 0x00000004
+#define HV_FLUSH_USE_EXTENDED_RANGE_FORMAT 0x00000008
+
/* Hypercall interface */
union hv_hypercall_input {
u64 as_uint64;
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index a8b4765..16a9221 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -240,6 +240,7 @@ static void __init ms_hyperv_init_platform(void)
* Setup the hook to get control post apic initialization.
*/
x86_platform.apic_post_init = hyperv_init;
+ hyperv_setup_mmu_ops();
#endif
}

--
2.9.4