linux-kernel - Re: [PATCH 5/6] KVM: selftests: memslot_perf

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Date:   Mon, 17 Oct 2022 23:36:04 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, kvmarm@...ts.linux.dev,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        ajones@...tanamicro.com, pbonzini@...hat.com, maz@...nel.org,
        shuah@...nel.org, oliver.upton@...ux.dev, seanjc@...gle.com,
        peterx@...hat.com, ricarkol@...gle.com, zhenyzha@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH 5/6] KVM: selftests: memslot_perf_test: Consolidate memory
 sizes

On 14.10.2022 09:19, Gavin Shan wrote:
> The addresses and sizes passed to madvise() and vm_userspace_mem_region_add()
> should be aligned to host page size, which can be 64KB on aarch64. So it's
> wrong by passing additional fixed 4KB memory area to various tests.
> 
> Fix it by passing additional fixed 64KB memory area to various tests. After
> it's applied, the following command works fine on 64KB-page-size-host and
> 4KB-page-size-guest.
> 
>    # ./memslot_perf_test -v -s 512
> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>   .../testing/selftests/kvm/memslot_perf_test.c  | 18 ++++++++++--------
>   1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/memslot_perf_test.c b/tools/testing/selftests/kvm/memslot_perf_test.c
> index d587bd952ff9..e6d34744b45d 100644
> --- a/tools/testing/selftests/kvm/memslot_perf_test.c
> +++ b/tools/testing/selftests/kvm/memslot_perf_test.c
> @@ -25,12 +25,14 @@
>   #include <kvm_util.h>
>   #include <processor.h>
>   
> -#define MEM_SIZE		((512U << 20) + 4096)
> -#define MEM_GPA		0x10000000UL
> +#define MEM_EXTRA_SIZE		0x10000

So the biggest page size supported right now is 64 KiB - it would be
good to have an assert somewhere to explicitly check for this
(regardless of implicit checks present in other calculations).

Also, an expression like "(64 << 10)" is more readable than a "1"
with a tail of zeroes (it's easy to add one zero too many or be one
zero short).

Thanks,
Maciej