Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section shared in RMP table

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On 1/5/22 2:27 PM, Dave Hansen wrote:
On 1/5/22 11:52, Brijesh Singh wrote:
          for (; vaddr < vaddr_end; vaddr += PMD_SIZE) {
+            /*
+             * When SEV-SNP is active then transition the page to shared in the RMP +             * table so that it is consistent with the page table attribute change.
+             */
+            early_snp_set_memory_shared(__pa(vaddr), __pa(vaddr), PTRS_PER_PMD);

Shouldn't the first argument be vaddr as below?

Nope, sme_postprocess_startup() is called while we are fixing the initial page table and running with identity mapping (so va == pa).

I'm not sure I've ever seen a line of code that wanted a comment so badly.

The early_snp_set_memory_shared() call the PVALIDATE instruction to clear the validated bit from the BSS region. The PVALIDATE instruction needs a virtual address, so we need to use the identity mapped virtual address so that PVALIDATE can clear the validated bit. I will add more comments to clarify it.

-Brijesh



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