linux-kernel - Re: [PATCH v4 07/10] KVM: selftests: Support multiple vCPUs in demand paging test

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Date:   Fri, 24 Jan 2020 11:49:43 +0100
From:   Andrew Jones <drjones@...hat.com>
To:     Ben Gardon <bgardon@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Cannon Matthews <cannonmatthews@...gle.com>,
        Peter Xu <peterx@...hat.com>, Peter Shier <pshier@...gle.com>,
        Oliver Upton <oupton@...gle.com>
Subject: Re: [PATCH v4 07/10] KVM: selftests: Support multiple vCPUs in
 demand paging test

On Thu, Jan 23, 2020 at 10:04:33AM -0800, Ben Gardon wrote:
...
> -static struct kvm_vm *create_vm(enum vm_guest_mode mode, uint32_t vcpuid,
> -				uint64_t extra_mem_pages, void *guest_code)
> +#define PAGE_SHIFT_4K  12
> +#define PTES_PER_4K_PT 512
> +
> +static struct kvm_vm *create_vm(enum vm_guest_mode mode, int vcpus,
> +				uint64_t vcpu_memory_bytes)
>  {
>  	struct kvm_vm *vm;
> -	uint64_t extra_pg_pages = extra_mem_pages / 512 * 2;
> +	uint64_t pages = DEFAULT_GUEST_PHY_PAGES;
> +
> +	/* Account for a few pages per-vCPU for stacks */
> +	pages += DEFAULT_STACK_PGS * vcpus;
> +
> +	/*
> +	 * Reserve twice the ammount of memory needed to map the test region and
> +	 * the page table / stacks region, at 4k, for page tables. Do the
> +	 * calculation with 4K page size: the smallest of all archs. (e.g., 64K
> +	 * page size guest will need even less memory for page tables).
> +	 */
> +	pages += (2 * pages) / PTES_PER_4K_PT;
> +	pages += ((2 * vcpus * vcpu_memory_bytes) >> PAGE_SHIFT_4K) /
> +		 PTES_PER_4K_PT;

pages needs to be rounded up to the next multiple of 16 in order for this
to work on aarch64 machines with 64k pages.

Thanks,
drew