Hi,
On Wed, Jan 17 2024, Alexander Graf wrote:
> When we have a KHO kexec, we get a device tree, mem cache and scratch
> region to populate the state of the system. Provide helper functions
> that allow architecture code to easily handle memory reservations based
> on them and give device drivers visibility into the KHO DT and memory
> reservations so they can recover their own state.
>
> Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>
>
> ---
>
[...]
> +/**
> + * kho_return_mem - Notify the kernel that initially reserved memory is no
> + * longer needed. When the last consumer of a page returns their mem, kho
> + * returns the page to the buddy allocator as free page.
> + */
> +void kho_return_mem(const struct kho_mem *mem)
> +{
> + uint64_t start_pfn, end_pfn, pfn;
> +
> + start_pfn = PFN_DOWN(mem->addr);
> + end_pfn = PFN_UP(mem->addr + mem->len);
> +
> + for (pfn = start_pfn; pfn < end_pfn; pfn++)
> + kho_return_pfn(pfn);
> +}
> +EXPORT_SYMBOL_GPL(kho_return_mem);
> +
> +static void kho_claim_pfn(ulong pfn)
> +{
> + struct page *page = pfn_to_page(pfn);
> +
> + WARN_ON(!page);
> + if (WARN_ON(page_count(page) != 1))
> + pr_err("Claimed non kho pfn %lx", pfn);
You do sanity checks but then never actually change anything on the
page. kho_claim_mem()'s documentation says: "This function removes the
reserved state for all pages that the mem spans". So this function
should at the very least call ClearPageReserved().
Also, checking the page count is a very rough heuristic. There can be
other non-KHO pages with page count == 1. Do you think it would make
more sense to use one of the private pageflags bits to mark a page
KHO-owned? If not, shouldn't you at least also check if the page is
reserved?
> +}
> +
> +/**
> + * kho_claim_mem - Notify the kernel that a handed over memory range is now in
> + * use by a kernel subsystem and considered an allocated page. This function
> + * removes the reserved state for all pages that the mem spans.
> + */
> +void *kho_claim_mem(const struct kho_mem *mem)
> +{
> + u64 start_pfn, end_pfn, pfn;
> + void *va = __va(mem->addr);
> +
> + start_pfn = PFN_DOWN(mem->addr);
> + end_pfn = PFN_UP(mem->addr + mem->len);
> +
> + for (pfn = start_pfn; pfn < end_pfn; pfn++)
> + kho_claim_pfn(pfn);
> +
> + return va;
> +}
> +EXPORT_SYMBOL_GPL(kho_claim_mem);
> +
[...]
--
Regards,
Pratyush Yadav
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
