2019-03-22 10:20:02

by Suthikulpanit, Suravee

Subject: [PATCH] svm/avic: Fix invalidate logical APIC id entry

Only clear the valid bit when invalidate logical APIC id entry.
The current logic clear the valid bit, but also set the rest of
the bits (including reserved bits) to 1.

Fixes: 98d90582be2e ('svm: Fix AVIC DFR and LDR handling')
Signed-off-by: Suravee Suthikulpanit <[email protected]>
---
arch/x86/kvm/svm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 7a4ce1a22ca0..f4fb766e474c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -4640,7 +4640,7 @@ static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
u32 *entry = avic_get_logical_id_entry(vcpu, svm->ldr_reg, flat);

if (entry)
- WRITE_ONCE(*entry, (u32) ~AVIC_LOGICAL_ID_ENTRY_VALID_MASK);
+ WRITE_ONCE(*entry, (u32)(*entry & ~AVIC_LOGICAL_ID_ENTRY_VALID_MASK));
}

static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
--
2.17.1

2019-03-22 13:05:11

by Vitaly Kuznetsov

Subject: Re: [PATCH] svm/avic: Fix invalidate logical APIC id entry

"Suthikulpanit, Suravee" <[email protected]> writes:

> Only clear the valid bit when invalidate logical APIC id entry.
> The current logic clear the valid bit, but also set the rest of
> the bits (including reserved bits) to 1.
>
> Fixes: 98d90582be2e ('svm: Fix AVIC DFR and LDR handling')
> Signed-off-by: Suravee Suthikulpanit <[email protected]>
> ---
> arch/x86/kvm/svm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 7a4ce1a22ca0..f4fb766e474c 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -4640,7 +4640,7 @@ static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
> u32 *entry = avic_get_logical_id_entry(vcpu, svm->ldr_reg, flat);
>
> if (entry)
> - WRITE_ONCE(*entry, (u32) ~AVIC_LOGICAL_ID_ENTRY_VALID_MASK);
> + WRITE_ONCE(*entry, (u32)(*entry & ~AVIC_LOGICAL_ID_ENTRY_VALID_MASK));

I'm not sure how important this is, but this change creates a tiny time
window between reading from *entry and writing there. Should we use
atomic bitops instead?

> }
>
> static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)

--
Vitaly

2019-03-26 03:50:05

by Suthikulpanit, Suravee

Subject: Re: [PATCH] svm/avic: Fix invalidate logical APIC id entry

On 3/22/19 8:04 PM, Vitaly Kuznetsov wrote:
> "Suthikulpanit, Suravee" <[email protected]> writes:
>
>> Only clear the valid bit when invalidate logical APIC id entry.
>> The current logic clear the valid bit, but also set the rest of
>> the bits (including reserved bits) to 1.
>>
>> Fixes: 98d90582be2e ('svm: Fix AVIC DFR and LDR handling')
>> Signed-off-by: Suravee Suthikulpanit <[email protected]>
>> ---
>> arch/x86/kvm/svm.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
>> index 7a4ce1a22ca0..f4fb766e474c 100644
>> --- a/arch/x86/kvm/svm.c
>> +++ b/arch/x86/kvm/svm.c
>> @@ -4640,7 +4640,7 @@ static void avic_invalidate_logical_id_entry(struct kvm_vcpu *vcpu)
>> u32 *entry = avic_get_logical_id_entry(vcpu, svm->ldr_reg, flat);
>>
>> if (entry)
>> - WRITE_ONCE(*entry, (u32) ~AVIC_LOGICAL_ID_ENTRY_VALID_MASK);
>> + WRITE_ONCE(*entry, (u32)(*entry & ~AVIC_LOGICAL_ID_ENTRY_VALID_MASK));
>
> I'm not sure how important this is, but this change creates a tiny time
> window between reading from *entry and writing there. Should we use
> atomic bitops instead?

Sure. That is also simpler. I'll send out V2 w/ clear_bit() instead.

Suravee

>
>> }
>>
>> static int avic_handle_ldr_update(struct kvm_vcpu *vcpu)
>