linux-kernel - Re: [PATCHv5 10/16] x86/tdx: Convert shared memory back to private on kexec

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Date: Fri, 5 Jan 2024 19:38:48 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com"
	<mingo@...hat.com>, "x86@...nel.org" <x86@...nel.org>, "bp@...en8.de"
	<bp@...en8.de>, "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
CC: "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>, "Reshetova,
 Elena" <elena.reshetova@...el.com>, "Nakajima, Jun" <jun.nakajima@...el.com>,
	"rafael@...nel.org" <rafael@...nel.org>, "peterz@...radead.org"
	<peterz@...radead.org>, "Huang, Kai" <kai.huang@...el.com>,
	"sathyanarayanan.kuppuswamy@...ux.intel.com"
	<sathyanarayanan.kuppuswamy@...ux.intel.com>, "Hunter, Adrian"
	<adrian.hunter@...el.com>, "thomas.lendacky@....com"
	<thomas.lendacky@....com>, "ashish.kalra@....com" <ashish.kalra@....com>,
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
	"seanjc@...gle.com" <seanjc@...gle.com>, "bhe@...hat.com" <bhe@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 10/16] x86/tdx: Convert shared memory back to private on
 kexec

The break apart looks good.

On Sat, 2023-12-23 at 02:52 +0300, Kirill A. Shutemov wrote:
> +       while (addr < end) {
> +               unsigned long size;
> +               unsigned int level;
> +               pte_t *pte;
> +
> +               pte = lookup_address(addr, &level);
> +               size = page_level_size(level);
> +
> +               if (pte && pte_decrypted(*pte)) {
> +                       int pages = size / PAGE_SIZE;
> +
> +                       /*
> +                        * Touching memory with shared bit set
> triggers implicit
> +                        * conversion to shared.
> +                        *
> +                        * Make sure nobody touches the shared range
> from
> +                        * now on.
> +                        */
> +                       set_pte(pte, __pte(0));

Does this need a full shootdown at this point, at least in the crash
case? A local flush for the non-crash case might be nice too.

Also, probably a barrier() between set_pte() and
tdx_enc_status_changed().

> +
> +                       if (!tdx_enc_status_changed(addr, pages,
> true)) {
> +                               pr_err("Failed to unshare range %#lx-
> %#lx\n",
> +                                      addr, addr + size);
> +                       }