[PATCH v2 0/2] arm: cpu: Add optional CMOs by VA

[PATCH v2 0/2] arm: cpu: Add optional CMOs by VA

[Ying-Chun Liu (PaulLiu)]

Exposing set/way cache maintenance to a virtual machine is unsafe, not
least because the instructions are not permission-checked but also
because they are not broadcast between CPUs. Consequently, KVM traps and
emulates such maintenance in the host kernel using by-VA operations and
looping over the stage-2 page-tables. However, when running under
protected KVM, these instructions are not able to be emulated and will
instead result in an exception being delivered to the guest.

Introduce CONFIG_CMO_BY_VA_ONLY so that virtual platforms can select
this option and perform by-VA cache maintenance instead of using the
set/way instructions.

Marc Zyngier (1):
  arm: cpu: Add optional CMOs by VA

Pierre-Clément Tosi (1):
  arm64: Initialize TLB memory if CMO_BY_VA_ONLY

v2: Fix the Signed-off-by list.

 arch/arm/cpu/armv8/Kconfig    |  4 ++
 arch/arm/cpu/armv8/cache.S    | 50 +++++++++++++-----
 arch/arm/cpu/armv8/cache_v8.c | 97 ++++++++++++++++++++++++++++++++++-
 arch/arm/cpu/armv8/cpu.c      | 30 +++++++----
 arch/arm/lib/cache.c          |  9 ++++
 5 files changed, 164 insertions(+), 26 deletions(-)

-- 
2.39.1

[PATCH v2 1/2] arm: cpu: Add optional CMOs by VA

[Ying-Chun Liu (PaulLiu)]

From: Marc Zyngier <maz@kernel.org>

Exposing set/way cache maintenance to a virtual machine is unsafe, not
least because the instructions are not permission-checked but also
because they are not broadcast between CPUs. Consequently, KVM traps and
emulates such maintenance in the host kernel using by-VA operations and
looping over the stage-2 page-tables. However, when running under
protected KVM, these instructions are not able to be emulated and will
instead result in an exception being delivered to the guest.

Introduce CONFIG_CMO_BY_VA_ONLY so that virtual platforms can select
this option and perform by-VA cache maintenance instead of using the
set/way instructions.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <willdeacon@google.com>
Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
[ Paul: pick from the Android tree. Fixup Pierre's commit. And fix some
  checkpatch warnings. Rebased to upstream. ]
Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Link: https://android.googlesource.com/platform/external/u-boot/+/db5507f47f4f57f766d52f753ff2cc761afc213b
Link: https://android.googlesource.com/platform/external/u-boot/+/2baf54e743380a1e4a6bc2dbdde020a2e783ff67
---
v2: Fix the Signed-off-by list.
---
 arch/arm/cpu/armv8/Kconfig    |  4 ++
 arch/arm/cpu/armv8/cache.S    | 50 +++++++++++++-----
 arch/arm/cpu/armv8/cache_v8.c | 97 ++++++++++++++++++++++++++++++++++-
 arch/arm/cpu/armv8/cpu.c      | 30 +++++++----
 4 files changed, 155 insertions(+), 26 deletions(-)

diff --git a/arch/arm/cpu/armv8/Kconfig b/arch/arm/cpu/armv8/Kconfig
index 1305238c9d..7d5cf1594d 100644
--- a/arch/arm/cpu/armv8/Kconfig
+++ b/arch/arm/cpu/armv8/Kconfig
@@ -1,5 +1,9 @@
 if ARM64
 
+config CMO_BY_VA_ONLY
+	bool "Force cache maintenance to be exclusively by VA"
+	depends on !SYS_DISABLE_DCACHE_OPS
+
 config ARMV8_SPL_EXCEPTION_VECTORS
 	bool "Install crash dump exception vectors"
 	depends on SPL
diff --git a/arch/arm/cpu/armv8/cache.S b/arch/arm/cpu/armv8/cache.S
index d1cee23437..3fe935cf28 100644
--- a/arch/arm/cpu/armv8/cache.S
+++ b/arch/arm/cpu/armv8/cache.S
@@ -12,6 +12,7 @@
 #include <asm/system.h>
 #include <linux/linkage.h>
 
+#ifndef CONFIG_CMO_BY_VA_ONLY
 /*
  * void __asm_dcache_level(level)
  *
@@ -116,6 +117,41 @@ ENTRY(__asm_invalidate_dcache_all)
 ENDPROC(__asm_invalidate_dcache_all)
 .popsection
 
+.pushsection .text.__asm_flush_l3_dcache, "ax"
+WEAK(__asm_flush_l3_dcache)
+	mov	x0, #0			/* return status as success */
+	ret
+ENDPROC(__asm_flush_l3_dcache)
+.popsection
+
+.pushsection .text.__asm_invalidate_l3_icache, "ax"
+WEAK(__asm_invalidate_l3_icache)
+	mov	x0, #0			/* return status as success */
+	ret
+ENDPROC(__asm_invalidate_l3_icache)
+.popsection
+
+#else	/* CONFIG_CMO_BY_VA */
+
+/*
+ * Define these so that they actively clash with in implementation
+ * accidentally selecting CONFIG_CMO_BY_VA
+ */
+
+.pushsection .text.__asm_invalidate_l3_icache, "ax"
+ENTRY(__asm_invalidate_l3_icache)
+	mov	x0, xzr
+	ret
+ENDPROC(__asm_invalidate_l3_icache)
+.popsection
+.pushsection .text.__asm_flush_l3_dcache, "ax"
+ENTRY(__asm_flush_l3_dcache)
+	mov	x0, xzr
+	ret
+ENDPROC(__asm_flush_l3_dcache)
+.popsection
+#endif	/* CONFIG_CMO_BY_VA */
+
 /*
  * void __asm_flush_dcache_range(start, end)
  *
@@ -189,20 +225,6 @@ WEAK(__asm_invalidate_l3_dcache)
 ENDPROC(__asm_invalidate_l3_dcache)
 .popsection
 
-.pushsection .text.__asm_flush_l3_dcache, "ax"
-WEAK(__asm_flush_l3_dcache)
-	mov	x0, #0			/* return status as success */
-	ret
-ENDPROC(__asm_flush_l3_dcache)
-.popsection
-
-.pushsection .text.__asm_invalidate_l3_icache, "ax"
-WEAK(__asm_invalidate_l3_icache)
-	mov	x0, #0			/* return status as success */
-	ret
-ENDPROC(__asm_invalidate_l3_icache)
-.popsection
-
 /*
  * void __asm_switch_ttbr(ulong new_ttbr)
  *
diff --git a/arch/arm/cpu/armv8/cache_v8.c b/arch/arm/cpu/armv8/cache_v8.c
index 2a226fd063..f333ad8889 100644
--- a/arch/arm/cpu/armv8/cache_v8.c
+++ b/arch/arm/cpu/armv8/cache_v8.c
@@ -163,6 +163,83 @@ static u64 *find_pte(u64 addr, int level)
 	return NULL;
 }
 
+#ifdef CONFIG_CMO_BY_VA_ONLY
+static void __cmo_on_leaves(void (*cmo_fn)(unsigned long, unsigned long),
+			    u64 pte, int level, u64 base)
+{
+	u64 *ptep;
+	int i;
+
+	ptep = (u64 *)(pte & GENMASK_ULL(47, PAGE_SHIFT));
+	for (i = 0; i < PAGE_SIZE / sizeof(u64); i++) {
+		u64 end, va = base + i * BIT(level2shift(level));
+		u64 type, attrs;
+
+		pte = ptep[i];
+		type = pte & PTE_TYPE_MASK;
+		attrs = pte & PMD_ATTRINDX_MASK;
+		debug("PTE %llx at level %d VA %llx\n", pte, level, va);
+
+		/* Not valid? next! */
+		if (!(type & PTE_TYPE_VALID))
+			continue;
+
+		/* Not a leaf? Recurse on the next level */
+		if (!(type == PTE_TYPE_BLOCK ||
+		      (level == 3 && type == PTE_TYPE_PAGE))) {
+			__cmo_on_leaves(cmo_fn, pte, level + 1, va);
+			continue;
+		}
+
+		/*
+		 * From this point, this must be a leaf.
+		 *
+		 * Start excluding non memory mappings
+		 */
+		if (attrs != PTE_BLOCK_MEMTYPE(MT_NORMAL) &&
+		    attrs != PTE_BLOCK_MEMTYPE(MT_NORMAL_NC))
+			continue;
+
+		end = va + BIT(level2shift(level)) - 1;
+
+		/* No intersection with RAM? */
+		if (end < gd->ram_base ||
+		    va >= (gd->ram_base + gd->ram_size))
+			continue;
+
+		/*
+		 * OK, we have a partial RAM mapping. However, this
+		 * can cover *more* than the RAM. Yes, u-boot is
+		 * *that* braindead. Compute the intersection we care
+		 * about, and not a byte more.
+		 */
+		va = max(va, (u64)gd->ram_base);
+		end = min(end, gd->ram_base + gd->ram_size);
+
+		debug("Flush PTE %llx at level %d: %llx-%llx\n",
+		      pte, level, va, end);
+		cmo_fn(va, end);
+	}
+}
+
+static void apply_cmo_to_mappings(void (*cmo_fn)(unsigned long, unsigned long))
+{
+	u64 va_bits;
+	int sl = 0;
+
+	if (!gd->arch.tlb_addr)
+		return;
+
+	get_tcr(NULL, &va_bits);
+	if (va_bits < 39)
+		sl = 1;
+
+	__cmo_on_leaves(cmo_fn, gd->arch.tlb_addr, sl, 0);
+}
+#else
+static inline void apply_cmo_to_mappings(void *dummy) {}
+#endif
+
 /* Returns and creates a new full table (512 entries) */
 static u64 *create_table(void)
 {
@@ -447,8 +524,12 @@ __weak void mmu_setup(void)
  */
 void invalidate_dcache_all(void)
 {
+#ifndef CONFIG_CMO_BY_VA_ONLY
 	__asm_invalidate_dcache_all();
 	__asm_invalidate_l3_dcache();
+#else
+	apply_cmo_to_mappings(invalidate_dcache_range);
+#endif
 }
 
 /*
@@ -458,6 +539,7 @@ void invalidate_dcache_all(void)
  */
 inline void flush_dcache_all(void)
 {
+#ifndef CONFIG_CMO_BY_VA_ONLY
 	int ret;
 
 	__asm_flush_dcache_all();
@@ -466,6 +548,9 @@ inline void flush_dcache_all(void)
 		debug("flushing dcache returns 0x%x\n", ret);
 	else
 		debug("flushing dcache successfully.\n");
+#else
+	apply_cmo_to_mappings(flush_dcache_range);
+#endif
 }
 
 #ifndef CONFIG_SYS_DISABLE_DCACHE_OPS
@@ -520,9 +605,19 @@ void dcache_disable(void)
 	if (!(sctlr & CR_C))
 		return;
 
+	if (IS_ENABLED(CONFIG_CMO_BY_VA_ONLY)) {
+		/*
+		 * When invalidating by VA, do it *before* turning the MMU
+		 * off, so that at least our stack is coherent.
+		 */
+		flush_dcache_all();
+	}
+
 	set_sctlr(sctlr & ~(CR_C|CR_M));
 
-	flush_dcache_all();
+	if (!IS_ENABLED(CONFIG_CMO_BY_VA_ONLY))
+		flush_dcache_all();
+
 	__asm_invalidate_tlb_all();
 }
 
diff --git a/arch/arm/cpu/armv8/cpu.c b/arch/arm/cpu/armv8/cpu.c
index db5d460eb4..3c7f36ad8d 100644
--- a/arch/arm/cpu/armv8/cpu.c
+++ b/arch/arm/cpu/armv8/cpu.c
@@ -48,18 +48,26 @@ int cleanup_before_linux(void)
 
 	disable_interrupts();
 
-	/*
-	 * Turn off I-cache and invalidate it
-	 */
-	icache_disable();
-	invalidate_icache_all();
+	if (IS_ENABLED(CONFIG_CMO_BY_VA_ONLY)) {
+		/*
+		 * Disable D-cache.
+		 */
+		dcache_disable();
+	} else {
+		/*
+		 * Turn off I-cache and invalidate it
+		 */
+		icache_disable();
+		invalidate_icache_all();
 
-	/*
-	 * turn off D-cache
-	 * dcache_disable() in turn flushes the d-cache and disables MMU
-	 */
-	dcache_disable();
-	invalidate_dcache_all();
+		/*
+		 * turn off D-cache
+		 * dcache_disable() in turn flushes the d-cache and disables
+		 * MMU
+		 */
+		dcache_disable();
+		invalidate_dcache_all();
+	}
 
 	return 0;
 }
-- 
2.39.1

[PATCH v2 2/2] arm64: Initialize TLB memory if CMO_BY_VA_ONLY

[Ying-Chun Liu (PaulLiu)]

From: Pierre-Clément Tosi <ptosi@google.com>

Memory used to hold the page tables is allocated from the top of RAM
with no prior initialization and could therefore hold invalid data. As
invalidate_dcache_all() will be called before the MMU has been
initialized and as that function relies indirectly on the page tables
when using CMO_BY_VA_ONLY, these must be in a valid state from their
allocation.

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
[ Paul: pick from the Android tree. Fix checkpatch warnings, and rebased
  to the upstream. ]
Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Cc: Tom Rini <trini@konsulko.com>
Link: https://android.googlesource.com/platform/external/u-boot/+/e3ceef4230b772186c6853cace4a676a407e6ab7
---
v2: Fix the Signed-off-by list.
---
 arch/arm/lib/cache.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm/lib/cache.c b/arch/arm/lib/cache.c
index 1a589c7e2a..7a16015867 100644
--- a/arch/arm/lib/cache.c
+++ b/arch/arm/lib/cache.c
@@ -159,6 +159,15 @@ __weak int arm_reserve_mmu(void)
 	 */
 	gd->arch.tlb_allocated = gd->arch.tlb_addr;
 #endif
+
+	if (IS_ENABLED(CONFIG_CMO_BY_VA_ONLY)) {
+		/*
+		 * As invalidate_dcache_all() will be called before
+		 * mmu_setup(), we should make sure that the PTs are
+		 * already in a valid state.
+		 */
+		memset((void *)gd->arch.tlb_addr, 0, gd->arch.tlb_size);
+	}
 #endif
 
 	return 0;
-- 
2.39.1

Re: [PATCH v2 1/2] arm: cpu: Add optional CMOs by VA

[Tom Rini]

[-- Attachment #1: Type: text/plain, Size: 1449 bytes --]

On Thu, Feb 09, 2023 at 04:54:27AM +0800, Ying-Chun Liu (PaulLiu) wrote:

> From: Marc Zyngier <maz@kernel.org>
> 
> Exposing set/way cache maintenance to a virtual machine is unsafe, not
> least because the instructions are not permission-checked but also
> because they are not broadcast between CPUs. Consequently, KVM traps and
> emulates such maintenance in the host kernel using by-VA operations and
> looping over the stage-2 page-tables. However, when running under
> protected KVM, these instructions are not able to be emulated and will
> instead result in an exception being delivered to the guest.
> 
> Introduce CONFIG_CMO_BY_VA_ONLY so that virtual platforms can select
> this option and perform by-VA cache maintenance instead of using the
> set/way instructions.
> 
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Signed-off-by: Will Deacon <willdeacon@google.com>
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> [ Paul: pick from the Android tree. Fixup Pierre's commit. And fix some
>   checkpatch warnings. Rebased to upstream. ]
> Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
> Cc: Tom Rini <trini@konsulko.com>
> Link: https://android.googlesource.com/platform/external/u-boot/+/db5507f47f4f57f766d52f753ff2cc761afc213b
> Link: https://android.googlesource.com/platform/external/u-boot/+/2baf54e743380a1e4a6bc2dbdde020a2e783ff67

Applied to u-boot/next, thanks!

-- 
Tom

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 659 bytes --]

Re: [PATCH v2 2/2] arm64: Initialize TLB memory if CMO_BY_VA_ONLY

[Tom Rini]

[-- Attachment #1: Type: text/plain, Size: 919 bytes --]

On Thu, Feb 09, 2023 at 04:54:28AM +0800, Ying-Chun Liu (PaulLiu) wrote:

> From: Pierre-Clément Tosi <ptosi@google.com>
> 
> Memory used to hold the page tables is allocated from the top of RAM
> with no prior initialization and could therefore hold invalid data. As
> invalidate_dcache_all() will be called before the MMU has been
> initialized and as that function relies indirectly on the page tables
> when using CMO_BY_VA_ONLY, these must be in a valid state from their
> allocation.
> 
> Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
> [ Paul: pick from the Android tree. Fix checkpatch warnings, and rebased
>   to the upstream. ]
> Signed-off-by: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
> Cc: Tom Rini <trini@konsulko.com>
> Link: https://android.googlesource.com/platform/external/u-boot/+/e3ceef4230b772186c6853cace4a676a407e6ab7

Applied to u-boot/next, thanks!

-- 
Tom

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 659 bytes --]