| Date | Thu, 3 Mar 2022 09:09:37 -0800 | From | Dave Hansen <> | Subject | Re: [PATCH v11 22/45] x86/sev: Use SEV-SNP AP creation to start secondary CPUs |
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On 2/24/22 08:56, Brijesh Singh wrote: > + /* > + * Allocate VMSA page to work around the SNP erratum where the CPU will > + * incorrectly signal an RMP violation #PF if a large page (2MB or 1GB) > + * collides with the RMP entry of VMSA page. The recommended workaround > + * is to not use a large page. > + * > + * Allocate one extra page, use a page which is not 2MB-aligned > + * and free the other. > + */ > + p = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_ZERO, 1); > + if (!p) > + return NULL; > + > + split_page(p, 1); > + > + pfn = page_to_pfn(p); > + if (IS_ALIGNED(__pfn_to_phys(pfn), PMD_SIZE)) { > + pfn++; > + __free_page(p); > + } else { > + __free_page(pfn_to_page(pfn + 1)); > + } > + > + return page_address(pfn_to_page(pfn)); > +}
This can be simplified. There's no need for all the sill pfn_to_page() conversions or even an alignment check. The second page (page[1]) of an order-1 page is never 2M/1G aligned. Just use that:
// Alloc an 8k page which is also 8k-aligned: p = alloc_pages(GFP_KERNEL_ACCOUNT | __GFP_ZERO, 1); if (!p) return NULL;
split_page(p, 1);
// Free the first 4k. This page _may_ // be 2M/1G aligned and can not be used: __free_page(p); // Return the unaligned page: return page_address(p+1);
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