[v5,1/2] KVM: Switch 'requests' to be 64-bit (explicitly)
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Message ID 1531214840-24686-1-git-send-email-karahmed@amazon.de
State New
Headers show

Commit Message

KarimAllah Ahmed July 10, 2018, 9:27 a.m. UTC
Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
use the size of "requests" instead of the hard-coded '32'.

That gives us a bit more room again for arch-specific requests as we
already ran out of space for x86 due to the hard-coded check.

The only exception here is ARM32 as it is still 32-bits.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: kvm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
---
v1 -> v2:
- Use FIELD_SIZEOF
---
 include/linux/kvm_host.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

Comments

Radim Krčmář July 18, 2018, 3:34 p.m. UTC | #1
2018-07-10 11:27+0200, KarimAllah Ahmed:
> Switch 'requests' to be explicitly 64-bit and update BUILD_BUG_ON check to
> use the size of "requests" instead of the hard-coded '32'.
> 
> That gives us a bit more room again for arch-specific requests as we
> already ran out of space for x86 due to the hard-coded check.
> 
> The only exception here is ARM32 as it is still 32-bits.

What do you mean?

I think we're just going to slow down kvm_request_pending() on 32 bit
architectures.

> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Reviewed-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> ---
> v1 -> v2:
> - Use FIELD_SIZEOF
> ---
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> @@ -130,7 +130,7 @@ static inline bool is_error_page(struct page *page)
>  #define KVM_REQUEST_ARCH_BASE     8

Now that the base is easily moveable, we could also lower it to 4 and
get few more arch flags.

Bumping requests to 64 bits is probably inevitable and this patch looks
good.

In v4, you have proposed the bitmap-array solution that would easily
allow more than 64 requests -- was the problem that possible
implementations of kvm_request_pending were not as efficient for current
amount of requests?

Thanks.

>  #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
> -	BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
> +	BUILD_BUG_ON((unsigned)(nr) >= (FIELD_SIZEOF(struct kvm_vcpu, requests) * 8) - KVM_REQUEST_ARCH_BASE); \
>  	(unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
>  })
>  #define KVM_ARCH_REQ(nr)           KVM_ARCH_REQ_FLAGS(nr, 0)

Patch
diff mbox

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 4ee7bc5..64518a1 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -130,7 +130,7 @@  static inline bool is_error_page(struct page *page)
 #define KVM_REQUEST_ARCH_BASE     8
 
 #define KVM_ARCH_REQ_FLAGS(nr, flags) ({ \
-	BUILD_BUG_ON((unsigned)(nr) >= 32 - KVM_REQUEST_ARCH_BASE); \
+	BUILD_BUG_ON((unsigned)(nr) >= (FIELD_SIZEOF(struct kvm_vcpu, requests) * 8) - KVM_REQUEST_ARCH_BASE); \
 	(unsigned)(((nr) + KVM_REQUEST_ARCH_BASE) | (flags)); \
 })
 #define KVM_ARCH_REQ(nr)           KVM_ARCH_REQ_FLAGS(nr, 0)
@@ -224,7 +224,7 @@  struct kvm_vcpu {
 	int vcpu_id;
 	int srcu_idx;
 	int mode;
-	unsigned long requests;
+	u64 requests;
 	unsigned long guest_debug;
 
 	int pre_pcpu;
@@ -1124,7 +1124,7 @@  static inline void kvm_make_request(int req, struct kvm_vcpu *vcpu)
 	 * caller.  Paired with the smp_mb__after_atomic in kvm_check_request.
 	 */
 	smp_wmb();
-	set_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
+	set_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
 }
 
 static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
@@ -1134,12 +1134,12 @@  static inline bool kvm_request_pending(struct kvm_vcpu *vcpu)
 
 static inline bool kvm_test_request(int req, struct kvm_vcpu *vcpu)
 {
-	return test_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
+	return test_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
 }
 
 static inline void kvm_clear_request(int req, struct kvm_vcpu *vcpu)
 {
-	clear_bit(req & KVM_REQUEST_MASK, &vcpu->requests);
+	clear_bit(req & KVM_REQUEST_MASK, (void *)&vcpu->requests);
 }
 
 static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)