RE: [PATCH 2/2] x86/hyper-v: check for VP_INVAL in hyperv_flush_tlb_others()

[Michael Kelley (EOSG)]

From: Vitaly Kuznetsov   Monday, July 9, 2018 10:40 AM
> Commit 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI
>  enlightenment") pre-filled hv_vp_index with VP_INVAL so it is now
> (theoretically) possible to observe hv_cpu_number_to_vp_number()
> returning VP_INVAL. We need to check for that in hyperv_flush_tlb_others().
> 
> Not checking for VP_INVAL on the first call site where we do
> 
>  if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64)
> goto do_ex_hypercall;
> 
> is OK, in case we're eligible for non-ex hypercall we'll catch the
> issue later in for_each_cpu() cycle and in case we'll be doing ex-
> hypercall cpumask_to_vpset() will fail.
> 
> It would be nice to change hv_cpu_number_to_vp_number() return
> value's type to 'u32' but this will likely be a bigger change as
> all call sites need to be checked first.
> 
> Fixes: 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI 
> enlightenment")
> Signed-off-by: Vitaly Kuznetsov 
> ---
>  arch/x86/hyperv/mmu.c | 5 +
>  1 file changed, 5 insertions(+)

Reviewed-by: Michael Kelley 
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[PATCH 2/2] x86/hyper-v: check for VP_INVAL in hyperv_flush_tlb_others()

[Vitaly Kuznetsov]

Commit 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI
 enlightenment") pre-filled hv_vp_index with VP_INVAL so it is now
(theoretically) possible to observe hv_cpu_number_to_vp_number()
returning VP_INVAL. We need to check for that in hyperv_flush_tlb_others().

Not checking for VP_INVAL on the first call site where we do

 if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64)
goto do_ex_hypercall;

is OK, in case we're eligible for non-ex hypercall we'll catch the
issue later in for_each_cpu() cycle and in case we'll be doing ex-
hypercall cpumask_to_vpset() will fail.

It would be nice to change hv_cpu_number_to_vp_number() return
value's type to 'u32' but this will likely be a bigger change as
all call sites need to be checked first.

Fixes: 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI 
enlightenment")
Signed-off-by: Vitaly Kuznetsov 
---
 arch/x86/hyperv/mmu.c | 5 +
 1 file changed, 5 insertions(+)

diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
index 453d2355cd61..1147e1fed7ff 100644
--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -111,6 +111,11 @@ static void hyperv_flush_tlb_others(const struct cpumask 
*cpus,
 
for_each_cpu(cpu, cpus) {
vcpu = hv_cpu_number_to_vp_number(cpu);
+   if (vcpu == VP_INVAL) {
+   local_irq_restore(flags);
+   goto do_native;
+   }
+
if (vcpu >= 64)
goto do_ex_hypercall;
 
-- 
2.14.4

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