linux-kernel - Re: [PATCH 06/20] KVM: selftests: Read per-page value into local var when verifying dirty_log

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Message-ID: <beec72cefd8518aecbf3ecb652c8e79ba71ff266.camel@redhat.com>
Date: Tue, 17 Dec 2024 18:59:51 -0500
From: Maxim Levitsky <mlevitsk@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, Peter Xu
	 <peterx@...hat.com>
Subject: Re: [PATCH 06/20] KVM: selftests: Read per-page value into local
 var when verifying dirty_log_test

On Fri, 2024-12-13 at 17:07 -0800, Sean Christopherson wrote:
> Cache the page's value during verification in a local variable, re-reading
> from the pointer is ugly and error prone, e.g. allows for bugs like
> checking the pointer itself instead of the value.

You should note that there are no functional changes in this patch.

Besides this,

Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>

Best regards,
	Maxim Levitsky

> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  tools/testing/selftests/kvm/dirty_log_test.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index 08cbecd1a135..5a04a7bd73e0 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -520,11 +520,10 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  {
>  	uint64_t page, nr_dirty_pages = 0, nr_clean_pages = 0;
>  	uint64_t step = vm_num_host_pages(mode, 1);
> -	uint64_t *value_ptr;
>  	uint64_t min_iter = 0;
>  
>  	for (page = 0; page < host_num_pages; page += step) {
> -		value_ptr = host_test_mem + page * host_page_size;
> +		uint64_t val = *(uint64_t *)(host_test_mem + page * host_page_size);
>  
>  		/* If this is a special page that we were tracking... */
>  		if (__test_and_clear_bit_le(page, host_bmap_track)) {
> @@ -545,11 +544,10 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  			 * the corresponding page should be either the
>  			 * previous iteration number or the current one.
>  			 */
> -			matched = (*value_ptr == iteration ||
> -				   *value_ptr == iteration - 1);
> +			matched = (val == iteration || val == iteration - 1);
>  
>  			if (host_log_mode == LOG_MODE_DIRTY_RING && !matched) {
> -				if (*value_ptr == iteration - 2 && min_iter <= iteration - 2) {
> +				if (val == iteration - 2 && min_iter <= iteration - 2) {
>  					/*
>  					 * Short answer: this case is special
>  					 * only for dirty ring test where the
> @@ -597,7 +595,7 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  			TEST_ASSERT(matched,
>  				    "Set page %"PRIu64" value %"PRIu64
>  				    " incorrect (iteration=%"PRIu64")",
> -				    page, *value_ptr, iteration);
> +				    page, val, iteration);
>  		} else {
>  			nr_clean_pages++;
>  			/*
> @@ -619,11 +617,11 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  			 *     we'll see that page P is cleared, with
>  			 *     value "iteration-1".
>  			 */
> -			TEST_ASSERT(*value_ptr <= iteration,
> +			TEST_ASSERT(val <= iteration,
>  				    "Clear page %"PRIu64" value %"PRIu64
>  				    " incorrect (iteration=%"PRIu64")",
> -				    page, *value_ptr, iteration);
> -			if (*value_ptr == iteration) {
> +				    page, val, iteration);
> +			if (val == iteration) {
>  				/*
>  				 * This page is _just_ modified; it
>  				 * should report its dirtyness in the