On 09/26/18 at 03:32pm, Baoquan He wrote: > On 09/25/18 at 07:26pm, Borislav Petkov wrote: > > IINM, the problem can be addressed in a simpler way by getting rid of > > enc_bit and thus getting rid of the need to do relative addressing of > > anything and simply doing the whole dance of figuring out the C-bit each > > time. It probably wouldn't be even measurable... > > Couldn't agree more. > > Obviously enc_bit is redundent here. We only check eax each time, > removing it can fix the RIP-relative addressing issue in kexec. OK, in distros CONFIG_AMD_MEM_ENCRYPT=y is set by default usually. enc_bit can save once in normal boot, then fetch and skip the cpuid detection in initialize_identity_maps(). However this only speeds up in amd system with SME, on intel cpu and amd cpu w/o sme, it still needs to do cpuid twice. Removing it should be not measurable as Boris said. Not sure if Tom has other concern. Thanks Baoquan > > diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S > index eaa843a52907..0b60eb867d25 100644 > --- a/arch/x86/boot/compressed/mem_encrypt.S > +++ b/arch/x86/boot/compressed/mem_encrypt.S > @@ -27,19 +27,6 @@ ENTRY(get_sev_encryption_bit) > push %edx > push %edi > > - /* > - * RIP-relative addressing is needed to access the encryption bit > - * variable. Since we are running in 32-bit mode we need this call/pop > - * sequence to get the proper relative addressing. > - */ > - call 1f > -1: popl %edi > - subl $1b, %edi > - > - movl enc_bit(%edi), %eax > - cmpl $0, %eax > - jge .Lsev_exit > - > /* Check if running under a hypervisor */ > movl $1, %eax > cpuid > @@ -69,12 +56,10 @@ ENTRY(get_sev_encryption_bit) > > movl %ebx, %eax > andl $0x3f, %eax /* Return the encryption bit location */ > - movl %eax, enc_bit(%edi) > jmp .Lsev_exit > > .Lno_sev: > xor %eax, %eax > - movl %eax, enc_bit(%edi) > > .Lsev_exit: > pop %edi > @@ -113,9 +98,6 @@ ENTRY(set_sev_encryption_mask) > ENDPROC(set_sev_encryption_mask) > > .data > -enc_bit: > - .int 0xffffffff > - > #ifdef CONFIG_AMD_MEM_ENCRYPT > .balign 8 > GLOBAL(sme_me_mask) _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
