On 12/13/21 at 09:02am, Christoph Hellwig wrote:

quoted

 
 ssize_t elfcorehdr_read(char *buf, size_t count, u64 *ppos)
 {
-	return read_from_oldmem(buf, count, ppos, 0,
+	struct kvec kvec = { .iov_base = buf, .iov_len = count };
+	struct iov_iter iter;
+
+	iov_iter_kvec(&iter, READ, &kvec, 1, count);
+
+	return read_from_oldmem(&iter, count, ppos,
 				cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT));
 }

elfcorehdr_read should probably also take an iov_iter while we're at it.

I also don't quite understand why we even need the arch overrides for it,
but that would require some digging into the history of this interface.

Below patchset removing sec_active() from generic code added this arch
override on x86_64. Before that, s390 and arm64 have had arch overrides. 
And arm64 says "elfcorehdr_read() is simple as the region is always mapped."
in commit e62aaeac42 "arm64: kdump: provide /proc/vmcore file".

[v3,0/6] Remove x86-specific code from generic headers
https://patchwork.kernel.org/project/linux-fsdevel/cover/20190718032858.28744-1-bauerman@linux.ibm.com/

5cbdaeefb655 s390/mm: Remove sev_active() function
ae7eb82a92fa fs/core/vmcore: Move sev_active() reference to x86 arch code
284e21fab2cf x86, s390/mm: Move sme_active() and sme_me_mask to x86-specific header
e740815a97e2 dma-mapping: Remove dma_check_mask()
47e5d8f9ed34 swiotlb: Remove call to sme_active()
0c9c1d563975 x86, s390: Move ARCH_HAS_MEM_ENCRYPT definition to arch/Kconfig