[PATCH] Use Little Endian for Dirty Bitmap

[PATCH] Use Little Endian for Dirty Bitmap

[Alexander Graf]

We currently use host endian long types to store information
in the dirty bitmap.

This works reasonably well on Little Endian targets, because the
u32 after the first contains the next 32 bits. On Big Endian this
breaks completely though, forcing us to be inventive here.

So Ben suggested to always use Little Endian, which looks reasonable.

We only have dirty bitmap implemented in Little Endian targets so far
and since PowerPC would be the first Big Endian platform, we can just
as well switch to Little Endian always with little effort without
breaking existing targets.

Signed-off-by: Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>
---
 virt/kvm/kvm_main.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 17d8688..3482ad1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -48,6 +48,7 @@
 #include <asm/io.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
+#include <asm-generic/bitops/le.h>
 
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
 #include "coalesced_mmio.h"
@@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
 
 		/* avoid RMW */
-		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
-			set_bit(rel_gfn, memslot->dirty_bitmap);
+		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
+			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
 	}
 }
 
-- 
1.6.0.2

--
To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

[PATCH] Use Little Endian for Dirty Bitmap

[Alexander Graf]

We currently use host endian long types to store information
in the dirty bitmap.

This works reasonably well on Little Endian targets, because the
u32 after the first contains the next 32 bits. On Big Endian this
breaks completely though, forcing us to be inventive here.

So Ben suggested to always use Little Endian, which looks reasonable.

We only have dirty bitmap implemented in Little Endian targets so far
and since PowerPC would be the first Big Endian platform, we can just
as well switch to Little Endian always with little effort without
breaking existing targets.

Signed-off-by: Alexander Graf <agraf@suse.de>
---
 virt/kvm/kvm_main.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 17d8688..3482ad1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -48,6 +48,7 @@
 #include <asm/io.h>
 #include <asm/uaccess.h>
 #include <asm/pgtable.h>
+#include <asm-generic/bitops/le.h>
 
 #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
 #include "coalesced_mmio.h"
@@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
 
 		/* avoid RMW */
-		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
-			set_bit(rel_gfn, memslot->dirty_bitmap);
+		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
+			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
 	}
 }
 
-- 
1.6.0.2

Re: [PATCH] Use Little Endian for Dirty Bitmap

[Alexander Graf]

bump

On 27.07.2009, at 12:38, Alexander Graf wrote:

> We currently use host endian long types to store information
> in the dirty bitmap.
>
> This works reasonably well on Little Endian targets, because the
> u32 after the first contains the next 32 bits. On Big Endian this
> breaks completely though, forcing us to be inventive here.
>
> So Ben suggested to always use Little Endian, which looks reasonable.
>
> We only have dirty bitmap implemented in Little Endian targets so far
> and since PowerPC would be the first Big Endian platform, we can just
> as well switch to Little Endian always with little effort without
> breaking existing targets.
>
> Signed-off-by: Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>
> ---
> virt/kvm/kvm_main.c |    5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 17d8688..3482ad1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -48,6 +48,7 @@
> #include <asm/io.h>
> #include <asm/uaccess.h>
> #include <asm/pgtable.h>
> +#include <asm-generic/bitops/le.h>
>
> #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
> #include "coalesced_mmio.h"
> @@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
> 		unsigned long rel_gfn = gfn - memslot->base_gfn;
>
> 		/* avoid RMW */
> -		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
> -			set_bit(rel_gfn, memslot->dirty_bitmap);
> +		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
> +			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
> 	}
> }
>
> -- 
> 1.6.0.2
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

--
To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] Use Little Endian for Dirty Bitmap

[Alexander Graf]

bump

On 27.07.2009, at 12:38, Alexander Graf wrote:

> We currently use host endian long types to store information
> in the dirty bitmap.
>
> This works reasonably well on Little Endian targets, because the
> u32 after the first contains the next 32 bits. On Big Endian this
> breaks completely though, forcing us to be inventive here.
>
> So Ben suggested to always use Little Endian, which looks reasonable.
>
> We only have dirty bitmap implemented in Little Endian targets so far
> and since PowerPC would be the first Big Endian platform, we can just
> as well switch to Little Endian always with little effort without
> breaking existing targets.
>
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
> virt/kvm/kvm_main.c |    5 +++--
> 1 files changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 17d8688..3482ad1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -48,6 +48,7 @@
> #include <asm/io.h>
> #include <asm/uaccess.h>
> #include <asm/pgtable.h>
> +#include <asm-generic/bitops/le.h>
>
> #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
> #include "coalesced_mmio.h"
> @@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
> 		unsigned long rel_gfn = gfn - memslot->base_gfn;
>
> 		/* avoid RMW */
> -		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
> -			set_bit(rel_gfn, memslot->dirty_bitmap);
> +		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
> +			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
> 	}
> }
>
> -- 
> 1.6.0.2
>
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] Use Little Endian for Dirty Bitmap

[Hollis Blanchard]

On Mon, 2009-07-27 at 12:38 +0200, Alexander Graf wrote:
> We currently use host endian long types to store information
> in the dirty bitmap.
> 
> This works reasonably well on Little Endian targets, because the
> u32 after the first contains the next 32 bits. On Big Endian this
> breaks completely though, forcing us to be inventive here.
> 
> So Ben suggested to always use Little Endian, which looks reasonable.
> 
> We only have dirty bitmap implemented in Little Endian targets so far
> and since PowerPC would be the first Big Endian platform, we can just
> as well switch to Little Endian always with little effort without
> breaking existing targets.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  virt/kvm/kvm_main.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 17d8688..3482ad1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -48,6 +48,7 @@
>  #include <asm/io.h>
>  #include <asm/uaccess.h>
>  #include <asm/pgtable.h>
> +#include <asm-generic/bitops/le.h>
> 
>  #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
>  #include "coalesced_mmio.h"
> @@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
>  		unsigned long rel_gfn = gfn - memslot->base_gfn;
> 
>  		/* avoid RMW */
> -		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
> -			set_bit(rel_gfn, memslot->dirty_bitmap);
> +		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
> +			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
>  	}
>  }

I don't think I've ever exercised the dirty bitmap code, and I don't
really have an opinion. Avi?

-- 
Hollis Blanchard
IBM Linux Technology Center

Re: [PATCH] Use Little Endian for Dirty Bitmap

[Hollis Blanchard]

On Mon, 2009-07-27 at 12:38 +0200, Alexander Graf wrote:
> We currently use host endian long types to store information
> in the dirty bitmap.
> 
> This works reasonably well on Little Endian targets, because the
> u32 after the first contains the next 32 bits. On Big Endian this
> breaks completely though, forcing us to be inventive here.
> 
> So Ben suggested to always use Little Endian, which looks reasonable.
> 
> We only have dirty bitmap implemented in Little Endian targets so far
> and since PowerPC would be the first Big Endian platform, we can just
> as well switch to Little Endian always with little effort without
> breaking existing targets.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  virt/kvm/kvm_main.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 17d8688..3482ad1 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -48,6 +48,7 @@
>  #include <asm/io.h>
>  #include <asm/uaccess.h>
>  #include <asm/pgtable.h>
> +#include <asm-generic/bitops/le.h>
> 
>  #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
>  #include "coalesced_mmio.h"
> @@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn)
>  		unsigned long rel_gfn = gfn - memslot->base_gfn;
> 
>  		/* avoid RMW */
> -		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
> -			set_bit(rel_gfn, memslot->dirty_bitmap);
> +		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
> +			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
>  	}
>  }

I don't think I've ever exercised the dirty bitmap code, and I don't
really have an opinion. Avi?

-- 
Hollis Blanchard
IBM Linux Technology Center

Re: [PATCH] Use Little Endian for Dirty Bitmap

[Alexander Graf]

On 29.09.2009, at 02:08, Hollis Blanchard wrote:

> On Mon, 2009-07-27 at 12:38 +0200, Alexander Graf wrote:
>> We currently use host endian long types to store information
>> in the dirty bitmap.
>>
>> This works reasonably well on Little Endian targets, because the
>> u32 after the first contains the next 32 bits. On Big Endian this
>> breaks completely though, forcing us to be inventive here.
>>
>> So Ben suggested to always use Little Endian, which looks reasonable.
>>
>> We only have dirty bitmap implemented in Little Endian targets so far
>> and since PowerPC would be the first Big Endian platform, we can just
>> as well switch to Little Endian always with little effort without
>> breaking existing targets.
>>
>> Signed-off-by: Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org>
>> ---
>> virt/kvm/kvm_main.c |    5 +++--
>> 1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 17d8688..3482ad1 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -48,6 +48,7 @@
>> #include <asm/io.h>
>> #include <asm/uaccess.h>
>> #include <asm/pgtable.h>
>> +#include <asm-generic/bitops/le.h>
>>
>> #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
>> #include "coalesced_mmio.h"
>> @@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t  
>> gfn)
>> 		unsigned long rel_gfn = gfn - memslot->base_gfn;
>>
>> 		/* avoid RMW */
>> -		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
>> -			set_bit(rel_gfn, memslot->dirty_bitmap);
>> +		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
>> +			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
>> 	}
>> }
>
> I don't think I've ever exercised the dirty bitmap code, and I don't
> really have an opinion. Avi?

No big endian kvm target currently implements dirty bitmaps. In fact,  
IIRC only x86 does atm. So by pinning it to LE now, we save ourselves  
from much trouble for any later user.

Alex

--
To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] Use Little Endian for Dirty Bitmap

[Alexander Graf]

On 29.09.2009, at 02:08, Hollis Blanchard wrote:

> On Mon, 2009-07-27 at 12:38 +0200, Alexander Graf wrote:
>> We currently use host endian long types to store information
>> in the dirty bitmap.
>>
>> This works reasonably well on Little Endian targets, because the
>> u32 after the first contains the next 32 bits. On Big Endian this
>> breaks completely though, forcing us to be inventive here.
>>
>> So Ben suggested to always use Little Endian, which looks reasonable.
>>
>> We only have dirty bitmap implemented in Little Endian targets so far
>> and since PowerPC would be the first Big Endian platform, we can just
>> as well switch to Little Endian always with little effort without
>> breaking existing targets.
>>
>> Signed-off-by: Alexander Graf <agraf@suse.de>
>> ---
>> virt/kvm/kvm_main.c |    5 +++--
>> 1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>> index 17d8688..3482ad1 100644
>> --- a/virt/kvm/kvm_main.c
>> +++ b/virt/kvm/kvm_main.c
>> @@ -48,6 +48,7 @@
>> #include <asm/io.h>
>> #include <asm/uaccess.h>
>> #include <asm/pgtable.h>
>> +#include <asm-generic/bitops/le.h>
>>
>> #ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
>> #include "coalesced_mmio.h"
>> @@ -1656,8 +1657,8 @@ void mark_page_dirty(struct kvm *kvm, gfn_t  
>> gfn)
>> 		unsigned long rel_gfn = gfn - memslot->base_gfn;
>>
>> 		/* avoid RMW */
>> -		if (!test_bit(rel_gfn, memslot->dirty_bitmap))
>> -			set_bit(rel_gfn, memslot->dirty_bitmap);
>> +		if (!generic_test_le_bit(rel_gfn, memslot->dirty_bitmap))
>> +			generic___set_le_bit(rel_gfn, memslot->dirty_bitmap);
>> 	}
>> }
>
> I don't think I've ever exercised the dirty bitmap code, and I don't
> really have an opinion. Avi?

No big endian kvm target currently implements dirty bitmaps. In fact,  
IIRC only x86 does atm. So by pinning it to LE now, we save ourselves  
from much trouble for any later user.

Alex