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Date: Sun, 2 Jun 2024 17:20:54 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, 
	Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org, "Rafael J. Wysocki" <rafael@kernel.org>, 
	Peter Zijlstra <peterz@infradead.org>, Adrian Hunter <adrian.hunter@intel.com>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>, Elena Reshetova <elena.reshetova@intel.com>, 
	Jun Nakajima <jun.nakajima@intel.com>, Rick Edgecombe <rick.p.edgecombe@intel.com>, 
	Tom Lendacky <thomas.lendacky@amd.com>, "Kalra, Ashish" <ashish.kalra@amd.com>, 
	Sean Christopherson <seanjc@google.com>, "Huang, Kai" <kai.huang@intel.com>, 
	Ard Biesheuvel <ardb@kernel.org>, Baoquan He <bhe@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, 
	"K. Y. Srinivasan" <kys@microsoft.com>, Haiyang Zhang <haiyangz@microsoft.com>, 
	kexec@lists.infradead.org, linux-hyperv@vger.kernel.org, linux-acpi@vger.kernel.org, 
	linux-coco@lists.linux.dev, linux-kernel@vger.kernel.org, Tao Liu <ltao@redhat.com>
Subject: Re: [PATCHv11 11/19] x86/tdx: Convert shared memory back to private
 on kexec
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References: <20240528095522.509667-1-kirill.shutemov@linux.intel.com>
 <20240528095522.509667-12-kirill.shutemov@linux.intel.com>
 <20240531151442.GMZlnpYkDCRlg1_YS0@fat_crate.local>
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On Fri, May 31, 2024 at 05:14:42PM +0200, Borislav Petkov wrote:
> On Tue, May 28, 2024 at 12:55:14PM +0300, Kirill A. Shutemov wrote:
> > +static void tdx_kexec_finish(void)
> > +{
> > +	unsigned long addr, end;
> > +	long found = 0, shared;
> > +
> > +	lockdep_assert_irqs_disabled();
> > +
> > +	addr = PAGE_OFFSET;
> > +	end  = PAGE_OFFSET + get_max_mapped();
> > +
> > +	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));
> > +
> 
> Format the below into a comment here:
> 
> /* 
> 
> The only thing one can do at this point on failure is panic. It is
> reasonable to proceed, especially for the crash case because the
> kexec-ed kernel is using a different page table so there won't be
> a mismatch between shared/private marking of the page so it doesn't
> matter.

Page tables would not make a difference here. We will switch to identity
mappings soon. And kexec-ed kernel will build new page tables from
scratch.

I will drop the part after "It is reasonable to proceed".


-- 
  Kiryl Shutsemau / Kirill A. Shutemov