On Thu, Jun 20, 2024 at 10:23:59PM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <[email protected]>
>
> SNP guests allocate shared buffers to perform I/O. It is done by
> allocating pages normally from the buddy allocator and converting them
> to shared with set_memory_decrypted().
>
> The second kernel has no idea what memory is converted this way. It only
The secon, kexec-ed, kernel...
> sees E820_TYPE_RAM.
...
> @@ -92,6 +94,9 @@ static struct ghcb *boot_ghcb __section(".data");
> /* Bitmap of SEV features supported by the hypervisor */
> static u64 sev_hv_features __ro_after_init;
>
> +/* Last address to be switched to private during kexec */
> +static unsigned long kexec_last_addr_to_make_private;
This is particularly yucky.
AFAIU, you want to:
1. Skip GHCB addresses when making all pages private
2. Once you're done converting, in snp_kexec_finish() go over the GHCB
addresses and convert them explicitly, one-by-one, without this silly
variable
> /* #VC handler runtime per-CPU data */
> struct sev_es_runtime_data {
> struct ghcb ghcb_page;
> @@ -1010,6 +1015,169 @@ void snp_accept_memory(phys_addr_t start, phys_addr_t
> end)
> set_pages_state(vaddr, npages, SNP_PAGE_STATE_PRIVATE);
> }
>
> +static bool set_pte_enc(pte_t *kpte, int level, void *va)
Code duplication: __set_clr_pte_enc().
You need to refactor the code instead of adding just another, generically
looking helper just because it is easier this way.
> +{
> + pte_t new_pte;
> +
> + if (pte_none(*kpte))
> + return false;
> +
> + /*
> + * Change the physical page attribute from C=0 to C=1. Flush the
> + * caches to ensure that data gets accessed with the correct C-bit.
> + */
> + if (pte_present(*kpte))
> + clflush_cache_range(va, page_level_size(level));
> +
> + new_pte = __pte(cc_mkenc(pte_val(*kpte)));
> + set_pte_atomic(kpte, new_pte);
> +
> + return true;
> +}
> +
> +static bool make_pte_private(pte_t *pte, unsigned long addr, int pages, int
> level)
> +{
> + struct sev_es_runtime_data *data;
> + struct ghcb *ghcb;
> +
> + data = this_cpu_read(runtime_data);
> + ghcb = &data->ghcb_page;
> +
> + /* Check for GHCB for being part of a PMD range. */
> + if ((unsigned long)ghcb >= addr &&
> + (unsigned long)ghcb <= (addr + (pages * PAGE_SIZE))) {
> + /*
> + * Ensure that the current cpu's GHCB is made private
s/cpu/CPU/g
There are multiple places.
> + * at the end of unshared loop so that we continue to use the
> + * optimized GHCB protocol and not force the switch to
> + * MSR protocol till the very end.
> + */
> + pr_debug("setting boot_ghcb to NULL for this cpu ghcb\n");
> + kexec_last_addr_to_make_private = addr;
> + return true;
> + }
> +
> + if (!set_pte_enc(pte, level, (void *)addr))
> + return false;
> +
> + snp_set_memory_private(addr, pages);
> +
> + return true;
> +}
> +
> +static void unshare_all_memory(void)
> +{
> + unsigned long addr, end;
> +
> + /*
> + * Walk direct mapping and convert all shared memory back to private,
This ends with a ','. Is anything more coming?
> + */
> +
> + 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);
> +
> + /*
> + * pte_none() check is required to skip physical memory holes
> in direct mapped.
This sentence needs to be written for humans. And come to think of it, you can
simply drop it. lookup_address() can return NULL so you simply need to check
its retval.
> + */
> + if (pte && pte_decrypted(*pte) && !pte_none(*pte)) {
> + int pages = size / PAGE_SIZE;
> +
> + if (!make_pte_private(pte, addr, pages, level)) {
> + pr_err("Failed to unshare range %#lx-%#lx\n",
> + addr, addr + size);
Might as well terminate the guest here.
> + }
> +
> + }
> +
> + addr += size;
> + }
> + __flush_tlb_all();
> +
> +}
> +
> +static void unshare_all_bss_decrypted_memory(void)
Why is this a separate function and not part of unshare_all_memory()?
> +{
> + unsigned long vaddr, vaddr_end;
> + unsigned int level;
> + unsigned int npages;
> + pte_t *pte;
> +
> + vaddr = (unsigned long)__start_bss_decrypted;
> + vaddr_end = (unsigned long)__start_bss_decrypted_unused;
> + npages = (vaddr_end - vaddr) >> PAGE_SHIFT;
> + for (; vaddr < vaddr_end; vaddr += PAGE_SIZE) {
> + pte = lookup_address(vaddr, &level);
> + if (!pte || !pte_decrypted(*pte) || pte_none(*pte))
> + continue;
> +
> + set_pte_enc(pte, level, (void *)vaddr);
> + }
> + vaddr = (unsigned long)__start_bss_decrypted;
> + snp_set_memory_private(vaddr, npages);
> +}
...
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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