Messages in this thread |  | | Subject | Re: [PATCH v8 13/40] x86/kernel: Make the bss.decrypted section shared in RMP table | From | Tom Lendacky <> | Date | Thu, 6 Jan 2022 13:06:13 -0600 |
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On 1/6/22 11:40 AM, Venu Busireddy wrote: > On 2022-01-05 15:39:22 -0600, Brijesh Singh wrote: >> >> >> 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. > > Looking forward to see your final comments explaining this. I can't > still follow why, when PVALIDATE needs the virtual address, we are doing > a __pa() on the vaddr.
It's because of the phase of booting that the kernel is in. At this point, the kernel is running in identity mapped mode (VA == PA). The __start_bss_decrypted address is a regular kernel address, e.g. for the kernel I'm on it is 0xffffffffa7600000. Since the PVALIDATE instruction requires a valid virtual address, the code needs to perform a __pa() against __start_bss_decrypted to get the identity mapped virtual address that is currently in place.
It is not until the .Ljump_to_C_code label in head_64.S that the addressing switches from identity mapped to kernel addresses.
Thanks, Tom
> > Venu >
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