linux-kernel - Re: [PATCH 1/2] kho: add support for preserving vmalloc allocations

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Message-ID: <20250903125620.GG470103@nvidia.com>
Date: Wed, 3 Sep 2025 09:56:20 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Alexander Graf <graf@...zon.com>, Baoquan He <bhe@...hat.com>,
	Changyuan Lyu <changyuanl@...gle.com>, Chris Li <chrisl@...nel.org>,
	Pasha Tatashin <pasha.tatashin@...een.com>,
	Pratyush Yadav <pratyush@...nel.org>, kexec@...ts.infradead.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] kho: add support for preserving vmalloc allocations

On Wed, Sep 03, 2025 at 09:30:17AM +0300, Mike Rapoport wrote:
> +int kho_preserve_vmalloc(void *ptr, phys_addr_t *preservation)
> +{
> +	struct kho_vmalloc_chunk *chunk, *first_chunk;
> +	struct vm_struct *vm = find_vm_area(ptr);
> +	int err;
> +
> +	if (!vm)
> +		return -EINVAL;
> +
> +	/* we don't support HUGE_VMAP yet */
> +	if (get_vm_area_page_order(vm))
> +		return -EOPNOTSUPP;

This is a compatability problem.. Should have some way to indicate
that future kernels have an incompatible serialization so restore can
fail..

> +	chunk = new_vmalloc_chunk(NULL);
> +	if (!chunk)
> +		return -ENOMEM;
> +	first_chunk = chunk;
> +	first_chunk->hdr.total_pages = vm->nr_pages;
> +
> +	for (int i = 0; i < vm->nr_pages; i++) {
> +		phys_addr_t phys = page_to_phys(vm->pages[i]);
> +
> +		err = kho_preserve_phys(phys, PAGE_SIZE);

Don't call kho_preserve_phy if you already have a page! We should be
getting rid of kho_preserve_phys() :(

Jason