On 9/2/22 08:15, Sean Christopherson wrote:
>> for (i = 0; i < npages; i++) {
>> - page_virtual = kmap_atomic(pages[i]);
>> + page_virtual = kmap_local_page(pages[i]);
>> clflush_cache_range(page_virtual, PAGE_SIZE);
> SEV is 64-bit only, any reason not to go straight to page_address()?
Yes. page_address() is a hack. People get away with using it, but they
really shouldn't, especially when it is used on pages you didn't
allocate yourself.
IOW:
page = alloc_page(GFP_KERNEL);
ptr = page_address(page);
is fine. But:
page = alloc_page(GFP_HIGHUSER);
ptr = page_address(page);
even on something that's Kconfig'd 64-bit only is a no-no in my book.
The same goes for a generic-looking function like sev_clflush_pages()
where the pages come from who-knows-where.
It's incredibly useful for kernel accesses to random pages to be bounded
explicitly. Keeping the kmap() *API* in place means it can be used for
things other than highmem mappings (like protection keys). The kmap*()
family is a pretty thin wrapper around page_address() on 64-bit most of
the time anyway.
