Commit 25f8c778 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'x86_cpu_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull x86 cpuid updates from Borislav Petkov:

 - Enable the short string copies for CPUs which support them, in
   copy_user_enhanced_fast_string()

 - Avoid writing MSR_CSTAR on Intel due to TDX guests raising a #VE trap

* tag 'x86_cpu_for_v5.17_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/lib: Add fast-short-rep-movs check to copy_user_enhanced_fast_string()
  x86/cpu: Don't write CSTAR MSR on Intel CPUs
parents 308319e9 244122b4

arch/x86/kernel/cpu/common.c

+13 −2
Original line number Diff line number Diff line
@@ -1787,6 +1787,17 @@ EXPORT_PER_CPU_SYMBOL(__preempt_count); 


DEFINE_PER_CPU(unsigned long, cpu_current_top_of_stack) = TOP_OF_INIT_STACK;



static void wrmsrl_cstar(unsigned long val)

{

	/*

	 * Intel CPUs do not support 32-bit SYSCALL. Writing to MSR_CSTAR

	 * is so far ignored by the CPU, but raises a #VE trap in a TDX

	 * guest. Avoid the pointless write on all Intel CPUs.

	 */

	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)

		wrmsrl(MSR_CSTAR, val);

}



/* May not be marked __init: used by software suspend */

void syscall_init(void)

{
@@ -1794,7 +1805,7 @@ void syscall_init(void) 
	wrmsrl(MSR_LSTAR, (unsigned long)entry_SYSCALL_64);



#ifdef CONFIG_IA32_EMULATION

	wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);

	wrmsrl_cstar((unsigned long)entry_SYSCALL_compat);

	/*

	 * This only works on Intel CPUs.

	 * On AMD CPUs these MSRs are 32-bit, CPU truncates MSR_IA32_SYSENTER_EIP.
@@ -1806,7 +1817,7 @@ void syscall_init(void) 
		    (unsigned long)(cpu_entry_stack(smp_processor_id()) + 1));

	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, (u64)entry_SYSENTER_compat);

#else

	wrmsrl(MSR_CSTAR, (unsigned long)ignore_sysret);

	wrmsrl_cstar((unsigned long)ignore_sysret);

	wrmsrl_safe(MSR_IA32_SYSENTER_CS, (u64)GDT_ENTRY_INVALID_SEG);

	wrmsrl_safe(MSR_IA32_SYSENTER_ESP, 0ULL);

	wrmsrl_safe(MSR_IA32_SYSENTER_EIP, 0ULL);

arch/x86/lib/copy_user_64.S

+2 −2
Original line number Diff line number Diff line
@@ -200,8 +200,8 @@ EXPORT_SYMBOL(copy_user_generic_string) 
 */

SYM_FUNC_START(copy_user_enhanced_fast_string)

	ASM_STAC

	cmpl $64,%edx

	jb .L_copy_short_string	/* less then 64 bytes, avoid the costly 'rep' */

	/* CPUs without FSRM should avoid rep movsb for short copies */

	ALTERNATIVE "cmpl $64, %edx; jb .L_copy_short_string", "", X86_FEATURE_FSRM

	movl %edx,%ecx

1:	rep

	movsb