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
