From 5eb256fe165c6037cc5a8564ef05b24836d97ffb Mon Sep 17 00:00:00 2001
From: Luiz Souza <luiz@netgate.com>
Date: Fri, 23 Feb 2018 19:43:41 -0300
Subject: Revert "Revert "MFC r321899""

This reverts commit 364d23417fdf8cd90b896af94c6857c6ba13be8c.
---
 sys/amd64/amd64/elf_machdep.c  | 19 +++++++++++++++++++
 sys/amd64/amd64/initcpu.c      | 27 +++++++++++++++++++++++++++
 sys/amd64/include/md_var.h     |  5 ++++-
 sys/amd64/linux/linux_sysvec.c |  2 ++
 4 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/sys/amd64/amd64/elf_machdep.c b/sys/amd64/amd64/elf_machdep.c
index ca07adc..4e9476a 100644
--- a/sys/amd64/amd64/elf_machdep.c
+++ b/sys/amd64/amd64/elf_machdep.c
@@ -84,6 +84,25 @@ struct sysentvec elf64_freebsd_sysvec = {
 };
 INIT_SYSENTVEC(elf64_sysvec, &elf64_freebsd_sysvec);
 
+void
+amd64_lower_shared_page(struct sysentvec *sv)
+{
+	if (hw_lower_amd64_sharedpage != 0) {
+		sv->sv_maxuser -= PAGE_SIZE;
+		sv->sv_shared_page_base -= PAGE_SIZE;
+		sv->sv_usrstack -= PAGE_SIZE;
+		sv->sv_psstrings -= PAGE_SIZE;
+	}
+}
+
+/*
+ * Do this fixup before INIT_SYSENTVEC (SI_ORDER_ANY) because the latter
+ * uses the value of sv_shared_page_base.
+ */
+SYSINIT(elf64_sysvec_fixup, SI_SUB_EXEC, SI_ORDER_FIRST,
+	(sysinit_cfunc_t) amd64_lower_shared_page,
+	&elf64_freebsd_sysvec);
+
 static Elf64_Brandinfo freebsd_brand_info = {
 	.brand		= ELFOSABI_FREEBSD,
 	.machine	= EM_X86_64,
diff --git a/sys/amd64/amd64/initcpu.c b/sys/amd64/amd64/initcpu.c
index 63c0f20..ff3b6be 100644
--- a/sys/amd64/amd64/initcpu.c
+++ b/sys/amd64/amd64/initcpu.c
@@ -48,6 +48,11 @@ __FBSDID("$FreeBSD$");
 static int	hw_instruction_sse;
 SYSCTL_INT(_hw, OID_AUTO, instruction_sse, CTLFLAG_RD,
     &hw_instruction_sse, 0, "SIMD/MMX2 instructions available in CPU");
+static int	lower_sharedpage_init;
+int		hw_lower_amd64_sharedpage;
+SYSCTL_INT(_hw, OID_AUTO, lower_amd64_sharedpage, CTLFLAG_RDTUN,
+    &hw_lower_amd64_sharedpage, 0,
+   "Lower sharedpage to work around Ryzen issue with executing code near the top of user memory");
 /*
  * -1: automatic (default)
  *  0: keep enable CLFLUSH
@@ -122,6 +127,28 @@ init_amd(void)
 			wrmsr(0xc0011020, msr);
 		}
 	}
+
+	/*
+	 * Work around a problem on Ryzen that is triggered by executing
+	 * code near the top of user memory, in our case the signal
+	 * trampoline code in the shared page on amd64.
+	 *
+	 * This function is executed once for the BSP before tunables take
+	 * effect so the value determined here can be overridden by the
+	 * tunable.  This function is then executed again for each AP and
+	 * also on resume.  Set a flag the first time so that value set by
+	 * the tunable is not overwritten.
+	 *
+	 * The stepping and/or microcode versions should be checked after
+	 * this issue is fixed by AMD so that we don't use this mode if not
+	 * needed.
+	 */
+	if (lower_sharedpage_init == 0) {
+		lower_sharedpage_init = 1;
+		if (CPUID_TO_FAMILY(cpu_id) == 0x17) {
+			hw_lower_amd64_sharedpage = 1;
+		}
+	}
 }
 
 /*
diff --git a/sys/amd64/include/md_var.h b/sys/amd64/include/md_var.h
index 706ffc6..7a84631 100644
--- a/sys/amd64/include/md_var.h
+++ b/sys/amd64/include/md_var.h
@@ -34,12 +34,15 @@
 
 #include <x86/x86_var.h>
 
-extern  uint64_t *vm_page_dump;
+extern uint64_t	*vm_page_dump;
+extern int	hw_lower_amd64_sharedpage;
 
 struct	savefpu;
+struct	sysentvec;
 
 void	amd64_conf_fast_syscall(void);
 void	amd64_db_resume_dbreg(void);
+void	amd64_lower_shared_page(struct sysentvec *);
 void	amd64_syscall(struct thread *td, int traced);
 void	doreti_iret(void) __asm(__STRING(doreti_iret));
 void	doreti_iret_fault(void) __asm(__STRING(doreti_iret_fault));
diff --git a/sys/amd64/linux/linux_sysvec.c b/sys/amd64/linux/linux_sysvec.c
index f77c2c9..942819b 100644
--- a/sys/amd64/linux/linux_sysvec.c
+++ b/sys/amd64/linux/linux_sysvec.c
@@ -833,6 +833,8 @@ static void
 linux_vdso_install(void *param)
 {
 
+	amd64_lower_shared_page(&elf_linux_sysvec);
+
 	linux_szsigcode = (&_binary_linux_locore_o_end - 
 	    &_binary_linux_locore_o_start);
 
-- 
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