From: Joerg Roedel <jroedel@xxxxxxx> commit 4009a4ac82dd95b8cd2b62bd30019476983f0aff upstream. 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 virt-install started to add a tpm-crb device to the guest by default and proactively because, raisins: https://github.com/virt-manager/virt-manager/commit/eb58c09f488b0633ed1eea012cd311e48864401e and as that commit says, the default adding of a TPM can be disabled with "virt-install ... --tpm none". 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. [ bp: Massage and extend commit message. ] Fixes: d8aa7eea78a1 ('x86/mm: Add Secure Encrypted Virtualization (SEV) support') Signed-off-by: Joerg Roedel <jroedel@xxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Reviewed-by: Tom Lendacky <thomas.lendacky@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220321093351.23976-1-joro@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/lib/iomem.c | 65 ++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 57 insertions(+), 8 deletions(-) --- a/arch/x86/lib/iomem.c +++ b/arch/x86/lib/iomem.c @@ -22,7 +22,7 @@ static __always_inline void rep_movs(voi : "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 volat } 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 * } 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);
