linux-kernel - Re: [PATCH 2/6] KVM: selftests: Stash the host page size in a global in the guest

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Message-ID: <diqz1pnp34st.fsf@google.com>
Date: Mon, 29 Sep 2025 10:56:50 +0000
From: Ackerley Tng <ackerleytng@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Christian Borntraeger <borntraeger@...ux.ibm.com>, Janosch Frank <frankja@...ux.ibm.com>, 
	Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Hildenbrand <david@...hat.com>, Fuad Tabba <tabba@...gle.com>, 
	Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH 2/6] KVM: selftests: Stash the host page size in a global
 in the guest_memfd test

Sean Christopherson <seanjc@...gle.com> writes:

> Use a global variable to track the host page size in the guest_memfd test
> so that the information doesn't need to be constantly passed around.  The
> state is purely a reflection of the underlying system, i.e. can't be set
> by the test and is constant for a given invocation of the test, and thus
> explicitly passing the host page size to individual testcases adds no
> value, e.g. doesn't allow testing different combinations.
>

I was going to pass in page_size to each of these test cases to test
HugeTLB support, that's how page_size crept into the parameters of these
functions.

Could we do a getpagesize() within the gmem_test() macro that you
introduced instead?

Reviewed-by: Ackerley Tng <ackerleytng@...gle.com>

> Making page_size a global will simplify an upcoming change to create a new
> guest_memfd instance per testcase.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  .../testing/selftests/kvm/guest_memfd_test.c  | 37 +++++++++----------
>  1 file changed, 18 insertions(+), 19 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/guest_memfd_test.c b/tools/testing/selftests/kvm/guest_memfd_test.c
> index 81b11a958c7a..8251d019206a 100644
> --- a/tools/testing/selftests/kvm/guest_memfd_test.c
> +++ b/tools/testing/selftests/kvm/guest_memfd_test.c
> @@ -24,6 +24,8 @@
>  #include "test_util.h"
>  #include "ucall_common.h"
>  
> +static size_t page_size;
> +
>  static void test_file_read_write(int fd)
>  {
>  	char buf[64];
> @@ -38,7 +40,7 @@ static void test_file_read_write(int fd)
>  		    "pwrite on a guest_mem fd should fail");
>  }
>  
> -static void test_mmap_supported(int fd, size_t page_size, size_t total_size)
> +static void test_mmap_supported(int fd, size_t total_size)
>  {
>  	const char val = 0xaa;
>  	char *mem;
> @@ -78,7 +80,7 @@ void fault_sigbus_handler(int signum)
>  	siglongjmp(jmpbuf, 1);
>  }
>  
> 
> [...snip...]
>