[tip: x86/paravirt] x86/paravirt: Switch mixed paravirt/alternative calls to alternatives

From: tip-bot2 for Juergen Gross
Date: Thu Dec 14 2023 - 06:37:11 EST

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The following commit has been merged into the x86/paravirt branch of tip:

Commit-ID: 60bc276b129eef8113f9d9b0a5cd5ae7f4c90acb
Gitweb: https://git.kernel.org/tip/60bc276b129eef8113f9d9b0a5cd5ae7f4c90acb
Author: Juergen Gross <jgross@xxxxxxxx>
AuthorDate: Sun, 10 Dec 2023 07:21:37 +01:00
Committer: Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Sun, 10 Dec 2023 23:33:09 +01:00

x86/paravirt: Switch mixed paravirt/alternative calls to alternatives

Instead of stacking alternative and paravirt patching, use the new
ALT_FLAG_CALL flag to switch those mixed calls to pure alternative
handling.

Eliminate the need to be careful regarding the sequence of alternative
and paravirt patching.

[ bp: Touch up commit message. ]

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20231210062138.2417-5-jgross@xxxxxxxx
---
arch/x86/include/asm/alternative.h | 5 +--
arch/x86/include/asm/paravirt.h | 12 ++++----
arch/x86/include/asm/paravirt_types.h | 40 ++++++++++++++------------
arch/x86/kernel/alternative.c | 1 +-
arch/x86/kernel/callthunks.c | 17 +++++------
arch/x86/kernel/module.c | 20 +++----------
6 files changed, 44 insertions(+), 51 deletions(-)

diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
index 472334e..fcd20c6 100644
--- a/arch/x86/include/asm/alternative.h
+++ b/arch/x86/include/asm/alternative.h
@@ -89,6 +89,8 @@ struct alt_instr {
u8 replacementlen; /* length of new instruction */
} __packed;

+extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
+
/*
* Debug flag that can be tested to see whether alternative
* instructions were patched in already:
@@ -104,11 +106,10 @@ extern void apply_fineibt(s32 *start_retpoline, s32 *end_retpoine,
s32 *start_cfi, s32 *end_cfi);

struct module;
-struct paravirt_patch_site;

struct callthunk_sites {
s32 *call_start, *call_end;
- struct paravirt_patch_site *pv_start, *pv_end;
+ struct alt_instr *alt_start, *alt_end;
};

#ifdef CONFIG_CALL_THUNKS
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index f18bfa7..973c2ac 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -738,20 +738,20 @@ void native_pv_lock_init(void) __init;

#ifdef CONFIG_X86_64
#ifdef CONFIG_PARAVIRT_XXL
+#ifdef CONFIG_DEBUG_ENTRY

#define PARA_PATCH(off) ((off) / 8)
#define PARA_SITE(ptype, ops) _PVSITE(ptype, ops)
#define PARA_INDIRECT(addr) *addr(%rip)

-#ifdef CONFIG_DEBUG_ENTRY
.macro PARA_IRQ_save_fl
- PARA_SITE(PARA_PATCH(PV_IRQ_save_fl),
- ANNOTATE_RETPOLINE_SAFE;
- call PARA_INDIRECT(pv_ops+PV_IRQ_save_fl);)
+ ANNOTATE_RETPOLINE_SAFE;
+ call PARA_INDIRECT(pv_ops+PV_IRQ_save_fl);
.endm

-#define SAVE_FLAGS ALTERNATIVE "PARA_IRQ_save_fl;", "pushf; pop %rax;", \
- ALT_NOT_XEN
+#define SAVE_FLAGS ALTERNATIVE_2 "PARA_IRQ_save_fl;", \
+ "ALT_CALL_INSTR;", ALT_CALL_ALWAYS, \
+ "pushf; pop %rax;", ALT_NOT_XEN
#endif
#endif /* CONFIG_PARAVIRT_XXL */
#endif /* CONFIG_X86_64 */
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 166e961..9cad536 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -276,15 +276,11 @@ extern struct paravirt_patch_template pv_ops;
#define NATIVE_LABEL(a,x,b) "\n\t.globl " a #x "_" #b "\n" a #x "_" #b ":\n\t"

unsigned int paravirt_patch(u8 type, void *insn_buff, unsigned long addr, unsigned int len);
+#define paravirt_ptr(op) [paravirt_opptr] "m" (pv_ops.op)

int paravirt_disable_iospace(void);

-/*
- * This generates an indirect call based on the operation type number.
- * The type number, computed in PARAVIRT_PATCH, is derived from the
- * offset into the paravirt_patch_template structure, and can therefore be
- * freely converted back into a structure offset.
- */
+/* This generates an indirect call based on the operation type number. */
#define PARAVIRT_CALL \
ANNOTATE_RETPOLINE_SAFE \
"call *%[paravirt_opptr];"
@@ -317,12 +313,6 @@ int paravirt_disable_iospace(void);
* However, x86_64 also has to clobber all caller saved registers, which
* unfortunately, are quite a bit (r8 - r11)
*
- * The call instruction itself is marked by placing its start address
- * and size into the .parainstructions section, so that
- * apply_paravirt() in arch/i386/kernel/alternative.c can do the
- * appropriate patching under the control of the backend pv_init_ops
- * implementation.
- *
* Unfortunately there's no way to get gcc to generate the args setup
* for the call, and then allow the call itself to be generated by an
* inline asm. Because of this, we must do the complete arg setup and
@@ -421,14 +411,27 @@ int paravirt_disable_iospace(void);
__mask & __eax; \
})

-
+/*
+ * Use alternative patching for paravirt calls:
+ * - For replacing an indirect call with a direct one, use the "normal"
+ * ALTERNATIVE() macro with the indirect call as the initial code sequence,
+ * which will be replaced with the related direct call by using the
+ * ALT_FLAG_DIRECT_CALL special case and the "always on" feature.
+ * - In case the replacement is either a direct call or a short code sequence
+ * depending on a feature bit, the ALTERNATIVE_2() macro is being used.
+ * The indirect call is the initial code sequence again, while the special
+ * code sequence is selected with the specified feature bit. In case the
+ * feature is not active, the direct call is used as above via the
+ * ALT_FLAG_DIRECT_CALL special case and the "always on" feature.
+ */
#define ____PVOP_CALL(ret, op, call_clbr, extra_clbr, ...) \
({ \
PVOP_CALL_ARGS; \
PVOP_TEST_NULL(op); \
- asm volatile(paravirt_alt(PARAVIRT_CALL) \
+ asm volatile(ALTERNATIVE(PARAVIRT_CALL, ALT_CALL_INSTR, \
+ ALT_CALL_ALWAYS) \
: call_clbr, ASM_CALL_CONSTRAINT \
- : paravirt_type(op), \
+ : paravirt_ptr(op), \
##__VA_ARGS__ \
: "memory", "cc" extra_clbr); \
ret; \
@@ -439,10 +442,11 @@ int paravirt_disable_iospace(void);
({ \
PVOP_CALL_ARGS; \
PVOP_TEST_NULL(op); \
- asm volatile(ALTERNATIVE(paravirt_alt(PARAVIRT_CALL), \
- alt, cond) \
+ asm volatile(ALTERNATIVE_2(PARAVIRT_CALL, \
+ ALT_CALL_INSTR, ALT_CALL_ALWAYS, \
+ alt, cond) \
: call_clbr, ASM_CALL_CONSTRAINT \
- : paravirt_type(op), \
+ : paravirt_ptr(op), \
##__VA_ARGS__ \
: "memory", "cc" extra_clbr); \
ret; \
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 6573051..48938bc 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -160,7 +160,6 @@ extern s32 __retpoline_sites[], __retpoline_sites_end[];
extern s32 __return_sites[], __return_sites_end[];
extern s32 __cfi_sites[], __cfi_sites_end[];
extern s32 __ibt_endbr_seal[], __ibt_endbr_seal_end[];
-extern struct alt_instr __alt_instructions[], __alt_instructions_end[];
extern s32 __smp_locks[], __smp_locks_end[];
void text_poke_early(void *addr, const void *opcode, size_t len);

diff --git a/arch/x86/kernel/callthunks.c b/arch/x86/kernel/callthunks.c
index 57e5c2e..64ad2dd 100644
--- a/arch/x86/kernel/callthunks.c
+++ b/arch/x86/kernel/callthunks.c
@@ -233,14 +233,13 @@ patch_call_sites(s32 *start, s32 *end, const struct core_text *ct)
}

static __init_or_module void
-patch_paravirt_call_sites(struct paravirt_patch_site *start,
- struct paravirt_patch_site *end,
- const struct core_text *ct)
+patch_alt_call_sites(struct alt_instr *start, struct alt_instr *end,
+ const struct core_text *ct)
{
- struct paravirt_patch_site *p;
+ struct alt_instr *a;

- for (p = start; p < end; p++)
- patch_call((void *)&p->instr_offset + p->instr_offset, ct);
+ for (a = start; a < end; a++)
+ patch_call((void *)&a->instr_offset + a->instr_offset, ct);
}

static __init_or_module void
@@ -248,7 +247,7 @@ callthunks_setup(struct callthunk_sites *cs, const struct core_text *ct)
{
prdbg("Patching call sites %s\n", ct->name);
patch_call_sites(cs->call_start, cs->call_end, ct);
- patch_paravirt_call_sites(cs->pv_start, cs->pv_end, ct);
+ patch_alt_call_sites(cs->alt_start, cs->alt_end, ct);
prdbg("Patching call sites done%s\n", ct->name);
}

@@ -257,8 +256,8 @@ void __init callthunks_patch_builtin_calls(void)
struct callthunk_sites cs = {
.call_start = __call_sites,
.call_end = __call_sites_end,
- .pv_start = __parainstructions,
- .pv_end = __parainstructions_end
+ .alt_start = __alt_instructions,
+ .alt_end = __alt_instructions_end
};

if (!cpu_feature_enabled(X86_FEATURE_CALL_DEPTH))
diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
index 5f71a0c..e18914c 100644
--- a/arch/x86/kernel/module.c
+++ b/arch/x86/kernel/module.c
@@ -276,7 +276,7 @@ int module_finalize(const Elf_Ehdr *hdr,
struct module *me)
{
const Elf_Shdr *s, *alt = NULL, *locks = NULL,
- *para = NULL, *orc = NULL, *orc_ip = NULL,
+ *orc = NULL, *orc_ip = NULL,
*retpolines = NULL, *returns = NULL, *ibt_endbr = NULL,
*calls = NULL, *cfi = NULL;
char *secstrings = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
@@ -286,8 +286,6 @@ int module_finalize(const Elf_Ehdr *hdr,
alt = s;
if (!strcmp(".smp_locks", secstrings + s->sh_name))
locks = s;
- if (!strcmp(".parainstructions", secstrings + s->sh_name))
- para = s;
if (!strcmp(".orc_unwind", secstrings + s->sh_name))
orc = s;
if (!strcmp(".orc_unwind_ip", secstrings + s->sh_name))
@@ -304,14 +302,6 @@ int module_finalize(const Elf_Ehdr *hdr,
ibt_endbr = s;
}

- /*
- * See alternative_instructions() for the ordering rules between the
- * various patching types.
- */
- if (para) {
- void *pseg = (void *)para->sh_addr;
- apply_paravirt(pseg, pseg + para->sh_size);
- }
if (retpolines || cfi) {
void *rseg = NULL, *cseg = NULL;
unsigned int rsize = 0, csize = 0;
@@ -341,7 +331,7 @@ int module_finalize(const Elf_Ehdr *hdr,
void *aseg = (void *)alt->sh_addr;
apply_alternatives(aseg, aseg + alt->sh_size);
}
- if (calls || para) {
+ if (calls || alt) {
struct callthunk_sites cs = {};

if (calls) {
@@ -349,9 +339,9 @@ int module_finalize(const Elf_Ehdr *hdr,
cs.call_end = (void *)calls->sh_addr + calls->sh_size;
}

- if (para) {
- cs.pv_start = (void *)para->sh_addr;
- cs.pv_end = (void *)para->sh_addr + para->sh_size;
+ if (alt) {
+ cs.alt_start = (void *)alt->sh_addr;
+ cs.alt_end = (void *)alt->sh_addr + alt->sh_size;
}

callthunks_patch_module_calls(&cs, me);

Next message: tip-bot2 for Juergen Gross: "[tip: x86/paravirt] x86/paravirt: Move some functions and defines to alternative.c"
Previous message: tip-bot2 for Juergen Gross: "[tip: x86/paravirt] x86/alternative: Add indirect call patching"
In reply to: Juergen Gross: "[PATCH v6 4/5] x86/paravirt: switch mixed paravirt/alternative calls to alternative_2"
Next in thread: Juergen Gross: "[PATCH v6 5/5] x86/paravirt: remove no longer needed paravirt patching code"
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