[Minios-devel] [UNIKRAFT PATCH v3 6/8] plat/common: Add functionality to save and restore extended (x86) registers

[Florian Schmidt <florian.schmidt@xxxxxxxxx>]

On creation of a sw_ctx struct, allocate an area sufficiently large to
save all extended registers. On context switch, use the appropriate CPU
instruction to save and restore those registers to/from that area.

Signed-off-by: Florian Schmidt <florian.schmidt@xxxxxxxxx>
---
 plat/common/include/sw_ctx.h  |  8 +++++--
 plat/common/include/x86/cpu.h | 43 +++++++++++++++++++++++++++++++++++
 plat/common/sw_ctx.c          | 18 +++++++++++++--
 3 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/plat/common/include/sw_ctx.h b/plat/common/include/sw_ctx.h
index fae96beb..d52fe65b 100644
--- a/plat/common/include/sw_ctx.h
+++ b/plat/common/include/sw_ctx.h
@@ -35,11 +35,15 @@
 #define __PLAT_CMN_SW_CTX_H__
 
 #ifndef __ASSEMBLY__
+#include <stdint.h>
 #include <uk/plat/thread.h>
 
 struct sw_ctx {
-       unsigned long sp;  /* Stack pointer */
-       unsigned long ip;  /* Instruction pointer */
+       unsigned long sp;       /* Stack pointer */
+       unsigned long ip;       /* Instruction pointer */
+       uintptr_t extregs;      /* Pointer to an area to which extended
+                                * registers are saved on context switch.
+                                */
 };
 
 void sw_ctx_callbacks_init(struct ukplat_ctx_callbacks *ctx_cbs);
diff --git a/plat/common/include/x86/cpu.h b/plat/common/include/x86/cpu.h
index 6de62dc0..8acd71e4 100644
--- a/plat/common/include/x86/cpu.h
+++ b/plat/common/include/x86/cpu.h
@@ -32,6 +32,7 @@
 
 #include <uk/arch/types.h>
 #include <x86/cpu_defs.h>
+#include <sw_ctx.h>
 #include <stdint.h>
 
 void halt(void);
@@ -55,6 +56,48 @@ struct _x86_features {
 
 extern struct _x86_features x86_cpu_features;
 
+static inline void save_extregs(struct sw_ctx *ctx)
+{
+       switch (x86_cpu_features.save) {
+       case X86_SAVE_NONE:
+               /* nothing to do */
+               break;
+       case X86_SAVE_FSAVE:
+               asm volatile("fsave (%0)" :: "r"(ctx->extregs) : "memory");
+               break;
+       case X86_SAVE_FXSAVE:
+               asm volatile("fxsave (%0)" :: "r"(ctx->extregs) : "memory");
+               break;
+       case X86_SAVE_XSAVE:
+               asm volatile("xsave (%0)" :: "r"(ctx->extregs),
+                               "a"(0xffffffff), "d"(0xffffffff) : "memory");
+               break;
+       case X86_SAVE_XSAVEOPT:
+               asm volatile("xsaveopt (%0)" :: "r"(ctx->extregs),
+                               "a"(0xffffffff), "d"(0xffffffff) : "memory");
+               break;
+       }
+}
+static inline void restore_extregs(struct sw_ctx *ctx)
+{
+       switch (x86_cpu_features.save) {
+       case X86_SAVE_NONE:
+               /* nothing to do */
+               break;
+       case X86_SAVE_FSAVE:
+               asm volatile("frstor (%0)" :: "r"(ctx->extregs));
+               break;
+       case X86_SAVE_FXSAVE:
+               asm volatile("fxrstor (%0)" :: "r"(ctx->extregs));
+               break;
+       case X86_SAVE_XSAVE:
+       case X86_SAVE_XSAVEOPT:
+               asm volatile("xrstor (%0)" :: "r"(ctx->extregs),
+                               "a"(0xffffffff), "d"(0xffffffff));
+               break;
+       }
+}
+
 static inline void _init_cpufeatures(void)
 {
        __u32 eax, ebx, ecx, edx;
diff --git a/plat/common/sw_ctx.c b/plat/common/sw_ctx.c
index a477753b..c69f5fde 100644
--- a/plat/common/sw_ctx.c
+++ b/plat/common/sw_ctx.c
@@ -32,12 +32,13 @@
  * THIS HEADER MAY NOT BE EXTRACTED OR MODIFIED IN ANY WAY.
  */
 
+#include <stdint.h>
 #include <stdlib.h>
 #include <uk/plat/thread.h>
 #include <uk/alloc.h>
 #include <sw_ctx.h>
 #include <uk/assert.h>
-
+#include <x86/cpu.h>
 
 static void *sw_ctx_create(struct uk_alloc *allocator, unsigned long sp);
 static void  sw_ctx_start(void *ctx) __noreturn;
@@ -52,10 +53,14 @@ extern void asm_thread_starter(void);
 static void *sw_ctx_create(struct uk_alloc *allocator, unsigned long sp)
 {
        struct sw_ctx *ctx;
+       size_t sz;
 
        UK_ASSERT(allocator != NULL);
 
-       ctx = uk_malloc(allocator, sizeof(struct sw_ctx));
+       sz = ALIGN_UP(sizeof(struct sw_ctx), x86_cpu_features.extregs_align)
+               + x86_cpu_features.extregs_size;
+       ctx = uk_malloc(allocator, sz);
+       uk_pr_debug("Allocating %lu bytes for sw ctx at %p\n", sz, ctx);
        if (ctx == NULL) {
                uk_pr_warn("Error allocating software context.");
                return NULL;
@@ -63,6 +68,10 @@ static void *sw_ctx_create(struct uk_alloc *allocator, 
unsigned long sp)
 
        ctx->sp = sp;
        ctx->ip = (unsigned long) asm_thread_starter;
+       ctx->extregs = ALIGN_UP(((uintptr_t)ctx + sizeof(struct sw_ctx)),
+                               x86_cpu_features.extregs_align);
+       // Initialize the extregs area by saving a valid register layout to it
+       save_extregs(ctx);
 
        return ctx;
 }
@@ -85,6 +94,11 @@ extern void asm_sw_ctx_switch(void *prevctx, void *nextctx);
 
 static void sw_ctx_switch(void *prevctx, void *nextctx)
 {
+       struct sw_ctx *p = prevctx;
+       struct sw_ctx *n = nextctx;
+
+       save_extregs(p);
+       restore_extregs(n);
        asm_sw_ctx_switch(prevctx, nextctx);
 }
 
-- 
2.20.1


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