linux-kernel - Re: [RFC V3 PATCH 6/6] sefltests: kvm: x86: Add selftest for private memory

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Date:   Thu, 6 Oct 2022 20:23:52 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vishal Annapurve <vannapurve@...gle.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, pbonzini@...hat.com,
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Subject: Re: [RFC V3 PATCH 6/6] sefltests: kvm: x86: Add selftest for private
 memory

On Fri, Aug 19, 2022, Vishal Annapurve wrote:
> +static bool verify_mem_contents(void *mem, uint32_t size, uint8_t pat)

As per feedback in v1[*], spell out "pattern".

[*] https://lore.kernel.org/all/YtiJx11AZHslcGnN@google.com

> +{
> +	uint8_t *buf = (uint8_t *)mem;
> +
> +	for (uint32_t i = 0; i < size; i++) {
> +		if (buf[i] != pat)
> +			return false;
> +	}
> +
> +	return true;
> +}
> +
> +/*
> + * Add custom implementation for memset to avoid using standard/builtin memset
> + * which may use features like SSE/GOT that don't work with guest vm execution
> + * within selftests.
> + */
> +void *memset(void *mem, int byte, size_t size)
> +{
> +	uint8_t *buf = (uint8_t *)mem;
> +
> +	for (uint32_t i = 0; i < size; i++)
> +		buf[i] = byte;
> +
> +	return buf;
> +}

memset(), memcpy(), and memcmp() are safe to use as of commit 6b6f71484bf4 ("KVM:
selftests: Implement memcmp(), memcpy(), and memset() for guest use").

Note the "fun" with gcc "optimizing" into infinite recursion... :-)

> +
> +static void populate_test_area(void *test_area_base, uint64_t pat)
> +{
> +	memset(test_area_base, pat, TEST_AREA_SIZE);
> +}
> +
> +static void populate_guest_test_mem(void *guest_test_mem, uint64_t pat)
> +{
> +	memset(guest_test_mem, pat, GUEST_TEST_MEM_SIZE);
> +}
> +
> +static bool verify_test_area(void *test_area_base, uint64_t area_pat,
> +	uint64_t guest_pat)

Again, avoid "pat".

> +{
> +	void *test_area1_base = test_area_base;
> +	uint64_t test_area1_size = GUEST_TEST_MEM_OFFSET;
> +	void *guest_test_mem = test_area_base + test_area1_size;
> +	uint64_t guest_test_size = GUEST_TEST_MEM_SIZE;
> +	void *test_area2_base = guest_test_mem + guest_test_size;
> +	uint64_t test_area2_size = (TEST_AREA_SIZE - (GUEST_TEST_MEM_OFFSET +
> +			GUEST_TEST_MEM_SIZE));

This is all amazingly hard to read.  AFAICT, the local variables are largely useless.
Actually, why even take in @test_area_base, isn't it hardcoded to TEST_AREA_GPA?
Then everything except the pattern can be hardcoded.

> +	return (verify_mem_contents(test_area1_base, test_area1_size, area_pat) &&
> +		verify_mem_contents(guest_test_mem, guest_test_size, guest_pat) &&
> +		verify_mem_contents(test_area2_base, test_area2_size, area_pat));
> +}