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SubjectRe: [PATCH 01/23] x86, kaiser: prepare assembly for entry/exit CR3 switching
On Tue, Oct 31, 2017 at 03:31:48PM -0700, Dave Hansen wrote:
> diff -puN arch/x86/entry/calling.h~kaiser-luto-base-cr3-work arch/x86/entry/calling.h
> --- a/arch/x86/entry/calling.h~kaiser-luto-base-cr3-work 2017-10-31 15:03:48.105007253 -0700
> +++ b/arch/x86/entry/calling.h 2017-10-31 15:03:48.113007631 -0700
> @@ -1,5 +1,6 @@
> #include <linux/jump_label.h>
> #include <asm/unwind_hints.h>
> +#include <asm/cpufeatures.h>
>
> /*
>
> @@ -217,6 +218,45 @@ For 32-bit we have the following convent
> #endif
> .endm
>
> +.macro ADJUST_KERNEL_CR3 reg:req
> +.endm
> +
> +.macro ADJUST_USER_CR3 reg:req
> +.endm
> +
> +.macro SWITCH_TO_KERNEL_CR3 scratch_reg:req
> + mov %cr3, \scratch_reg
> + ADJUST_KERNEL_CR3 \scratch_reg
> + mov \scratch_reg, %cr3
> +.endm
> +
> +.macro SWITCH_TO_USER_CR3 scratch_reg:req
> + mov %cr3, \scratch_reg
> + ADJUST_USER_CR3 \scratch_reg
> + mov \scratch_reg, %cr3
> +.endm
> +
> +.macro SAVE_AND_SWITCH_TO_KERNEL_CR3 scratch_reg:req save_reg:req
> + movq %cr3, %r\scratch_reg
> + movq %r\scratch_reg, \save_reg

So one of the args gets passed as "ax", for example, which then gets
completed to a register with the "%r" prepended and the other is a full
register: %r14.

What for? Can we stick with one format pls?

> + /*
> + * Just stick a random bit in here that never gets set. Fixed
> + * up in real KAISER patches in a moment.
> + */
> + bt $63, %r\scratch_reg
> + jz .Ldone_\@
> +
> + ADJUST_KERNEL_CR3 %r\scratch_reg
> + movq %r\scratch_reg, %cr3
> +
> +.Ldone_\@:
> +.endm
> +
> +.macro RESTORE_CR3 save_reg:req
> + /* optimize this */
> + movq \save_reg, %cr3
> +.endm
> +
> #endif /* CONFIG_X86_64 */
>
> /*
> diff -puN arch/x86/entry/entry_64_compat.S~kaiser-luto-base-cr3-work arch/x86/entry/entry_64_compat.S
> --- a/arch/x86/entry/entry_64_compat.S~kaiser-luto-base-cr3-work 2017-10-31 15:03:48.107007348 -0700
> +++ b/arch/x86/entry/entry_64_compat.S 2017-10-31 15:03:48.113007631 -0700
> @@ -48,8 +48,13 @@
> ENTRY(entry_SYSENTER_compat)
> /* Interrupts are off on entry. */
> SWAPGS_UNSAFE_STACK
> +
> movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
>
> + pushq %rdi
> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
> + popq %rdi

So we switch to kernel CR3 right after we've setup kernel stack...

> +
> /*
> * User tracing code (ptrace or signal handlers) might assume that
> * the saved RAX contains a 32-bit number when we're invoking a 32-bit
> @@ -91,6 +96,9 @@ ENTRY(entry_SYSENTER_compat)
> pushq $0 /* pt_regs->r15 = 0 */
> cld
>
> + pushq %rdi
> + SWITCH_TO_KERNEL_CR3 scratch_reg=%rdi
> + popq %rdi

... and switch here *again*, after pushing pt_regs?!? What's up?

> /*
> * SYSENTER doesn't filter flags, so we need to clear NT and AC
> * ourselves. To save a few cycles, we can check whether
--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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