Re: [PATCH v6 2/6] x86/tdx: Support vmalloc() for tdx_enc_status_changed()

[kirill . shutemov]

On Tue, May 23, 2023 at 01:39:11PM -0700, Dave Hansen wrote:
> On 5/4/23 15:53, Dexuan Cui wrote:
> > When a TDX guest runs on Hyper-V, the hv_netvsc driver's netvsc_init_buf()
> > allocates buffers using vzalloc(), and needs to share the buffers with the
> > host OS by calling set_memory_decrypted(), which is not working for
> > vmalloc() yet. Add the support by handling the pages one by one.
> 
> I think this sets a bad precedent.
> 
> There are consequences for converting pages between shared and private.
> Doing it on a vmalloc() mapping is guaranteed to fracture the underlying
> EPT/SEPT mappings.
> 
> How does this work with load_unaligned_zeropad()?  Couldn't it be
> running around poking at one of these vmalloc()'d pages via the direct
> map during a shared->private conversion before the page has been accepted?

Alias processing in __change_page_attr_set_clr() will change direct
mapping if you call it on vmalloc()ed memory. I think we are safe wrt
load_unaligned_zeropad() here.
-- 
  Kiryl Shutsemau / Kirill A. Shutemov