From: Joerg Roedel <jroedel@xxxxxxx>
The io specific memcpy/memset functions use string mmio accesses to do
their work. Under SEV the hypervisor can't emulate these instructions,
because they read/write directly from/to encrypted memory.
KVM will inject a page fault exception into the guest when it is asked
to emulate string mmio instructions for an SEV guest:
BUG: unable to handle page fault for address: ffffc90000065068
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 8000100000067 P4D 8000100000067 PUD 80001000fb067 PMD 80001000fc067 PTE 80000000fed40173
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.17.0-rc7 #3
As string mmio for an SEV guest can not be supported by the
hypervisor, unroll the instructions for CC_ATTR_GUEST_UNROLL_STRING_IO
enabled kernels.
This issue appears when kernels are launched in recent libvirt-managed
SEV virtual machines, because libvirt started to add a tpm-crb device
to the guest by default.
The kernel driver for tpm-crb uses memcpy_to/from_io() functions to
access MMIO memory, resulting in a page-fault injected by KVM and
crashing the kernel at boot.
Cc: stable@xxxxxxxxxxxxxxx #4.15+
Fixes: d8aa7eea78a1 ('x86/mm: Add Secure Encrypted Virtualization (SEV) support')
Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
Changes v2->v3:
- Fix sparse warnings introduced by v2
arch/x86/lib/iomem.c | 65 ++++++++++++++++++++++++++++++++++++++------
1 file changed, 57 insertions(+), 8 deletions(-)
diff --git a/arch/x86/lib/iomem.c b/arch/x86/lib/iomem.c
index df50451d94ef..3e2f33fc33de 100644
--- a/arch/x86/lib/iomem.c
+++ b/arch/x86/lib/iomem.c
@@ -22,7 +22,7 @@ static __always_inline void rep_movs(void *to, const void *from, size_t n)
: "memory");
}
-void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
+static void string_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
{
if (unlikely(!n))
return;
@@ -38,9 +38,8 @@ void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
}
rep_movs(to, (const void *)from, n);
}
-EXPORT_SYMBOL(memcpy_fromio);
-void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
+static void string_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
{
if (unlikely(!n))
return;
@@ -56,14 +55,64 @@ void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
}
rep_movs((void *)to, (const void *) from, n);
}
+
+static void unrolled_memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
+{
+ const volatile char __iomem *in = from;
+ char *out = to;
+ int i;
+
+ for (i = 0; i < n; ++i)
+ out[i] = readb(&in[i]);
+}
+
+static void unrolled_memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
+{
+ volatile char __iomem *out = to;
+ const char *in = from;
+ int i;
+
+ for (i = 0; i < n; ++i)
+ writeb(in[i], &out[i]);
+}
+
+static void unrolled_memset_io(volatile void __iomem *a, int b, size_t c)
+{
+ volatile char __iomem *mem = a;
+ int i;
+
+ for (i = 0; i < c; ++i)
+ writeb(b, &mem[i]);
+}
+
+void memcpy_fromio(void *to, const volatile void __iomem *from, size_t n)
+{
+ if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
+ unrolled_memcpy_fromio(to, from, n);
+ else
+ string_memcpy_fromio(to, from, n);
+}
+EXPORT_SYMBOL(memcpy_fromio);
+
+void memcpy_toio(volatile void __iomem *to, const void *from, size_t n)
+{
+ if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO))
+ unrolled_memcpy_toio(to, from, n);
+ else
+ string_memcpy_toio(to, from, n);
+}
EXPORT_SYMBOL(memcpy_toio);
void memset_io(volatile void __iomem *a, int b, size_t c)
{
- /*
- * TODO: memset can mangle the IO patterns quite a bit.
- * perhaps it would be better to use a dumb one:
- */
- memset((void *)a, b, c);
+ if (cc_platform_has(CC_ATTR_GUEST_UNROLL_STRING_IO)) {
+ unrolled_memset_io(a, b, c);
+ } else {
+ /*
+ * TODO: memset can mangle the IO patterns quite a bit.
+ * perhaps it would be better to use a dumb one:
+ */
+ memset((void *)a, b, c);
+ }
}
EXPORT_SYMBOL(memset_io);
--
2.35.1
