x86/hyperv: remove on-stack cpumask from hv_send_ipi_mask_allbutself

It is not a good practice to allocate a cpumask on stack, given it may
consume up to 1 kilobytes of stack space if the kernel is configured to
have 8192 cpus.

The internal helper functions __send_ipi_mask{,_ex} need to loop over
the provided mask anyway, so it is not too difficult to skip `self'
there. We can thus do away with the on-stack cpumask in
hv_send_ipi_mask_allbutself.

Adjust call sites of __send_ipi_mask as needed.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Suggested-by: Michael Kelley <mikelley@microsoft.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Fixes: 68bb7bfb7985d ("X86/Hyper-V: Enable IPI enlightenments")
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210910185714.299411-3-wei.liu@kernel.org

diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 90e682a..32a1ad3 100644 (file)
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -99,7 +99,8 @@ static void hv_apic_eoi_write(u32 reg, u32 val)
 /*
  * IPI implementation on Hyper-V.
  */
-static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector)
+static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector,
+               bool exclude_self)
 {
        struct hv_send_ipi_ex **arg;
        struct hv_send_ipi_ex *ipi_arg;
@@ -123,7 +124,10 @@ static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector)
 
        if (!cpumask_equal(mask, cpu_present_mask)) {
                ipi_arg->vp_set.format = HV_GENERIC_SET_SPARSE_4K;
-               nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);
+               if (exclude_self)
+                       nr_bank = cpumask_to_vpset_noself(&(ipi_arg->vp_set), mask);
+               else
+                       nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);
        }
        if (nr_bank < 0)
                goto ipi_mask_ex_done;
@@ -138,15 +142,25 @@ ipi_mask_ex_done:
        return hv_result_success(status);
 }
 
-static bool __send_ipi_mask(const struct cpumask *mask, int vector)
+static bool __send_ipi_mask(const struct cpumask *mask, int vector,
+               bool exclude_self)
 {
-       int cur_cpu, vcpu;
+       int cur_cpu, vcpu, this_cpu = smp_processor_id();
        struct hv_send_ipi ipi_arg;
        u64 status;
+       unsigned int weight;
 
        trace_hyperv_send_ipi_mask(mask, vector);
 
-       if (cpumask_empty(mask))
+       weight = cpumask_weight(mask);
+
+       /*
+        * Do nothing if
+        *   1. the mask is empty
+        *   2. the mask only contains self when exclude_self is true
+        */
+       if (weight == 0 ||
+           (exclude_self && weight == 1 && cpumask_test_cpu(this_cpu, mask)))
                return true;
 
        if (!hv_hypercall_pg)
@@ -172,6 +186,8 @@ static bool __send_ipi_mask(const struct cpumask *mask, int vector)
        ipi_arg.cpu_mask = 0;
 
        for_each_cpu(cur_cpu, mask) {
+               if (exclude_self && cur_cpu == this_cpu)
+                       continue;
                vcpu = hv_cpu_number_to_vp_number(cur_cpu);
                if (vcpu == VP_INVAL)
                        return false;
@@ -191,7 +207,7 @@ static bool __send_ipi_mask(const struct cpumask *mask, int vector)
        return hv_result_success(status);
 
 do_ex_hypercall:
-       return __send_ipi_mask_ex(mask, vector);
+       return __send_ipi_mask_ex(mask, vector, exclude_self);
 }
 
 static bool __send_ipi_one(int cpu, int vector)
@@ -208,7 +224,7 @@ static bool __send_ipi_one(int cpu, int vector)
                return false;
 
        if (vp >= 64)
-               return __send_ipi_mask_ex(cpumask_of(cpu), vector);
+               return __send_ipi_mask_ex(cpumask_of(cpu), vector, false);
 
        status = hv_do_fast_hypercall16(HVCALL_SEND_IPI, vector, BIT_ULL(vp));
        return hv_result_success(status);
@@ -222,20 +238,13 @@ static void hv_send_ipi(int cpu, int vector)
 
 static void hv_send_ipi_mask(const struct cpumask *mask, int vector)
 {
-       if (!__send_ipi_mask(mask, vector))
+       if (!__send_ipi_mask(mask, vector, false))
                orig_apic.send_IPI_mask(mask, vector);
 }
 
 static void hv_send_ipi_mask_allbutself(const struct cpumask *mask, int vector)
 {
-       unsigned int this_cpu = smp_processor_id();
-       struct cpumask new_mask;
-       const struct cpumask *local_mask;
-
-       cpumask_copy(&new_mask, mask);
-       cpumask_clear_cpu(this_cpu, &new_mask);
-       local_mask = &new_mask;
-       if (!__send_ipi_mask(local_mask, vector))
+       if (!__send_ipi_mask(mask, vector, true))
                orig_apic.send_IPI_mask_allbutself(mask, vector);
 }
 
@@ -246,7 +255,7 @@ static void hv_send_ipi_allbutself(int vector)
 
 static void hv_send_ipi_all(int vector)
 {
-       if (!__send_ipi_mask(cpu_online_mask, vector))
+       if (!__send_ipi_mask(cpu_online_mask, vector, false))
                orig_apic.send_IPI_all(vector);
 }