| Message ID | jpgy4iqi85i.fsf@linux.bootlegged.copy (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/09/15 00:42, Bandan Das wrote: > > If a Linux guest is assigned more memory than is supported > by the host processor, the guest is unable to boot. That > is expected, however, there's no message indicating the user > what went wrong. This change prints a message to stderr if > KVM has the corresponding capability. > > Reported-by: Laszlo Ersek <lersek@redhat.com> > Signed-off-by: Bandan Das <bsd@redhat.com> > --- > linux-headers/linux/kvm.h | 1 + > target-i386/kvm.c | 6 ++++++ > 2 files changed, 7 insertions(+) > > diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h > index 3bac873..6afad49 100644 > --- a/linux-headers/linux/kvm.h > +++ b/linux-headers/linux/kvm.h > @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { > #define KVM_CAP_DISABLE_QUIRKS 116 > #define KVM_CAP_X86_SMM 117 > #define KVM_CAP_MULTI_ADDRESS_SPACE 118 > +#define KVM_CAP_PHY_ADDR_WIDTH 119 > > #ifdef KVM_CAP_IRQ_ROUTING > > diff --git a/target-i386/kvm.c b/target-i386/kvm.c > index 066d03d..66e3448 100644 > --- a/target-i386/kvm.c > +++ b/target-i386/kvm.c > @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > uint64_t shadow_mem; > int ret; > struct utsname utsname; > + int max_phys_bits; > > ret = kvm_get_supported_msrs(s); > if (ret < 0) { > @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > } > } > > + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); > + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) > + fprintf(stderr, "Warning: The amount of memory assigned to the guest " > + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); > + > if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { > smram_machine_done.notify = register_smram_listener; > qemu_add_machine_init_done_notifier(&smram_machine_done); > First, see my comments on the KVM patch. Second, ram_size is not the right thing to compare. What should be checked is whether the highest guest-physical address that maps to RAM can be represented in the address width of the host processor (and only if EPT is enabled, but that sub-condition belongs to the KVM patch). Note that this is not the same as the check written in the patch. For example, if you assume a 32-bit PCI hole with size 1 GB, then a total guest RAM of size 63 GB will result in the highest guest-phys memory address being 0xF_FFFF_FFFF, which just fits into 36 bits. Correspondingly, the above code would not print the warning for -m $((63 * 1024 + 1)) on my laptop (which has "address sizes : 36 bits physical, ..."), even though such a guest would not boot for me (with EPT enabled). Please see http://thread.gmane.org/gmane.comp.bios.tianocore.devel/15418/focus=15447 So, "ram_size" in the controlling expression should be replaced with "maximum_guest_ram_address" (which should be inclusive, and the <= relop should be preserved). Thanks Laszlo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 09/07/2015 00:42, Bandan Das wrote: > > If a Linux guest is assigned more memory than is supported > by the host processor, the guest is unable to boot. That > is expected, however, there's no message indicating the user > what went wrong. This change prints a message to stderr if > KVM has the corresponding capability. > > Reported-by: Laszlo Ersek <lersek@redhat.com> > Signed-off-by: Bandan Das <bsd@redhat.com> This is not entirely correct, because it doesn't take the PCI hole into account. Perhaps KVM could simply hide memory above the limit (i.e. treat it as MMIO), and the BIOS could remove RAM above the limit from the e820 memory map? Paolo > --- > linux-headers/linux/kvm.h | 1 + > target-i386/kvm.c | 6 ++++++ > 2 files changed, 7 insertions(+) > > diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h > index 3bac873..6afad49 100644 > --- a/linux-headers/linux/kvm.h > +++ b/linux-headers/linux/kvm.h > @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { > #define KVM_CAP_DISABLE_QUIRKS 116 > #define KVM_CAP_X86_SMM 117 > #define KVM_CAP_MULTI_ADDRESS_SPACE 118 > +#define KVM_CAP_PHY_ADDR_WIDTH 119 > > #ifdef KVM_CAP_IRQ_ROUTING > > diff --git a/target-i386/kvm.c b/target-i386/kvm.c > index 066d03d..66e3448 100644 > --- a/target-i386/kvm.c > +++ b/target-i386/kvm.c > @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > uint64_t shadow_mem; > int ret; > struct utsname utsname; > + int max_phys_bits; > > ret = kvm_get_supported_msrs(s); > if (ret < 0) { > @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > } > } > > + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); > + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) > + fprintf(stderr, "Warning: The amount of memory assigned to the guest " > + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); > + > if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { > smram_machine_done.notify = register_smram_listener; > qemu_add_machine_init_done_notifier(&smram_machine_done); > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/09/15 09:59, Paolo Bonzini wrote: > > > On 09/07/2015 00:42, Bandan Das wrote: >> >> If a Linux guest is assigned more memory than is supported >> by the host processor, the guest is unable to boot. That >> is expected, however, there's no message indicating the user >> what went wrong. This change prints a message to stderr if >> KVM has the corresponding capability. >> >> Reported-by: Laszlo Ersek <lersek@redhat.com> >> Signed-off-by: Bandan Das <bsd@redhat.com> > > This is not entirely correct, because it doesn't take the PCI hole into > account. > > Perhaps KVM could simply hide memory above the limit (i.e. treat it as > MMIO), and the BIOS could remove RAM above the limit from the e820 > memory map? I'd prefer to leave the guest firmware*s* out of this... :) E820 is a legacy BIOS concept. In OVMF we'd have to hack the memory resource descriptor HOBs (which in turn control the DXE memory space map, which in turn controls the UEFI memory map). Those HOBs are currently based on what the CMOS reports about the RAM available under and above 4GB. It's pretty complex already (will get more complex with SMM support), and TBH, for working around such an obscure issue, I wouldn't like to complicate it even further... After all, this is a host platform limitation. The solution should be to either move to a more capable host, or do it in software (disable EPT). Thanks! Laszlo > > Paolo > >> --- >> linux-headers/linux/kvm.h | 1 + >> target-i386/kvm.c | 6 ++++++ >> 2 files changed, 7 insertions(+) >> >> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h >> index 3bac873..6afad49 100644 >> --- a/linux-headers/linux/kvm.h >> +++ b/linux-headers/linux/kvm.h >> @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { >> #define KVM_CAP_DISABLE_QUIRKS 116 >> #define KVM_CAP_X86_SMM 117 >> #define KVM_CAP_MULTI_ADDRESS_SPACE 118 >> +#define KVM_CAP_PHY_ADDR_WIDTH 119 >> >> #ifdef KVM_CAP_IRQ_ROUTING >> >> diff --git a/target-i386/kvm.c b/target-i386/kvm.c >> index 066d03d..66e3448 100644 >> --- a/target-i386/kvm.c >> +++ b/target-i386/kvm.c >> @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> uint64_t shadow_mem; >> int ret; >> struct utsname utsname; >> + int max_phys_bits; >> >> ret = kvm_get_supported_msrs(s); >> if (ret < 0) { >> @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> } >> } >> >> + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); >> + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) >> + fprintf(stderr, "Warning: The amount of memory assigned to the guest " >> + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); >> + >> if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { >> smram_machine_done.notify = register_smram_listener; >> qemu_add_machine_init_done_notifier(&smram_machine_done); >> -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, 09 Jul 2015 09:02:38 +0200 Laszlo Ersek <lersek@redhat.com> wrote: > On 07/09/15 00:42, Bandan Das wrote: > > > > If a Linux guest is assigned more memory than is supported > > by the host processor, the guest is unable to boot. That > > is expected, however, there's no message indicating the user > > what went wrong. This change prints a message to stderr if > > KVM has the corresponding capability. > > > > Reported-by: Laszlo Ersek <lersek@redhat.com> > > Signed-off-by: Bandan Das <bsd@redhat.com> > > --- > > linux-headers/linux/kvm.h | 1 + > > target-i386/kvm.c | 6 ++++++ > > 2 files changed, 7 insertions(+) > > > > diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h > > index 3bac873..6afad49 100644 > > --- a/linux-headers/linux/kvm.h > > +++ b/linux-headers/linux/kvm.h > > @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { > > #define KVM_CAP_DISABLE_QUIRKS 116 > > #define KVM_CAP_X86_SMM 117 > > #define KVM_CAP_MULTI_ADDRESS_SPACE 118 > > +#define KVM_CAP_PHY_ADDR_WIDTH 119 > > > > #ifdef KVM_CAP_IRQ_ROUTING > > > > diff --git a/target-i386/kvm.c b/target-i386/kvm.c > > index 066d03d..66e3448 100644 > > --- a/target-i386/kvm.c > > +++ b/target-i386/kvm.c > > @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > > uint64_t shadow_mem; > > int ret; > > struct utsname utsname; > > + int max_phys_bits; > > > > ret = kvm_get_supported_msrs(s); > > if (ret < 0) { > > @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > > } > > } > > > > + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); > > + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) > > + fprintf(stderr, "Warning: The amount of memory assigned to the guest " > > + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); > > + > > if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { > > smram_machine_done.notify = register_smram_listener; > > qemu_add_machine_init_done_notifier(&smram_machine_done); > > > > First, see my comments on the KVM patch. > > Second, ram_size is not the right thing to compare. What should be > checked is whether the highest guest-physical address that maps to RAM > can be represented in the address width of the host processor (and only > if EPT is enabled, but that sub-condition belongs to the KVM patch). > > Note that this is not the same as the check written in the patch. For > example, if you assume a 32-bit PCI hole with size 1 GB, then a total > guest RAM of size 63 GB will result in the highest guest-phys memory > address being 0xF_FFFF_FFFF, which just fits into 36 bits. > > Correspondingly, the above code would not print the warning for > > -m $((63 * 1024 + 1)) > > on my laptop (which has "address sizes : 36 bits physical, ..."), even > though such a guest would not boot for me (with EPT enabled). > > Please see > > http://thread.gmane.org/gmane.comp.bios.tianocore.devel/15418/focus=15447 > > So, "ram_size" in the controlling expression should be replaced with > "maximum_guest_ram_address" (which should be inclusive, and the <= relop > should be preserved). also with memory hotplug tuned on we should check if the end of hotplug memory area is less then limit, i.e.: pcms->hotplug_memory.base + hotplug_mem_size < 1ULL << max_phys_bits > > Thanks > Laszlo > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/09/15 11:27, Igor Mammedov wrote: > On Thu, 09 Jul 2015 09:02:38 +0200 > Laszlo Ersek <lersek@redhat.com> wrote: > >> On 07/09/15 00:42, Bandan Das wrote: >>> >>> If a Linux guest is assigned more memory than is supported >>> by the host processor, the guest is unable to boot. That >>> is expected, however, there's no message indicating the user >>> what went wrong. This change prints a message to stderr if >>> KVM has the corresponding capability. >>> >>> Reported-by: Laszlo Ersek <lersek@redhat.com> >>> Signed-off-by: Bandan Das <bsd@redhat.com> >>> --- >>> linux-headers/linux/kvm.h | 1 + >>> target-i386/kvm.c | 6 ++++++ >>> 2 files changed, 7 insertions(+) >>> >>> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h >>> index 3bac873..6afad49 100644 >>> --- a/linux-headers/linux/kvm.h >>> +++ b/linux-headers/linux/kvm.h >>> @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { >>> #define KVM_CAP_DISABLE_QUIRKS 116 >>> #define KVM_CAP_X86_SMM 117 >>> #define KVM_CAP_MULTI_ADDRESS_SPACE 118 >>> +#define KVM_CAP_PHY_ADDR_WIDTH 119 >>> >>> #ifdef KVM_CAP_IRQ_ROUTING >>> >>> diff --git a/target-i386/kvm.c b/target-i386/kvm.c >>> index 066d03d..66e3448 100644 >>> --- a/target-i386/kvm.c >>> +++ b/target-i386/kvm.c >>> @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >>> uint64_t shadow_mem; >>> int ret; >>> struct utsname utsname; >>> + int max_phys_bits; >>> >>> ret = kvm_get_supported_msrs(s); >>> if (ret < 0) { >>> @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >>> } >>> } >>> >>> + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); >>> + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) >>> + fprintf(stderr, "Warning: The amount of memory assigned to the guest " >>> + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); >>> + >>> if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { >>> smram_machine_done.notify = register_smram_listener; >>> qemu_add_machine_init_done_notifier(&smram_machine_done); >>> >> >> First, see my comments on the KVM patch. >> >> Second, ram_size is not the right thing to compare. What should be >> checked is whether the highest guest-physical address that maps to RAM >> can be represented in the address width of the host processor (and only >> if EPT is enabled, but that sub-condition belongs to the KVM patch). >> >> Note that this is not the same as the check written in the patch. For >> example, if you assume a 32-bit PCI hole with size 1 GB, then a total >> guest RAM of size 63 GB will result in the highest guest-phys memory >> address being 0xF_FFFF_FFFF, which just fits into 36 bits. >> >> Correspondingly, the above code would not print the warning for >> >> -m $((63 * 1024 + 1)) >> >> on my laptop (which has "address sizes : 36 bits physical, ..."), even >> though such a guest would not boot for me (with EPT enabled). >> >> Please see >> >> http://thread.gmane.org/gmane.comp.bios.tianocore.devel/15418/focus=15447 >> >> So, "ram_size" in the controlling expression should be replaced with >> "maximum_guest_ram_address" (which should be inclusive, and the <= relop >> should be preserved). > also with memory hotplug tuned on we should check if the end of > hotplug memory area is less then limit, i.e.: > > pcms->hotplug_memory.base + hotplug_mem_size < 1ULL << max_phys_bits Seems reasonable, thanks for the hint! (The LHS in this instance is exclusive though, so equality should *not* trigger the warning. "maximum_guest_ram_address" is inclusive, and equality should trigger the warning. (Although equality seems quite impossible in practice.)) Thanks! Laszlo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, 08 Jul 2015 18:42:01 -0400 Bandan Das <bsd@redhat.com> wrote: > > If a Linux guest is assigned more memory than is supported > by the host processor, the guest is unable to boot. That > is expected, however, there's no message indicating the user > what went wrong. This change prints a message to stderr if > KVM has the corresponding capability. > > Reported-by: Laszlo Ersek <lersek@redhat.com> > Signed-off-by: Bandan Das <bsd@redhat.com> > --- > linux-headers/linux/kvm.h | 1 + > target-i386/kvm.c | 6 ++++++ > 2 files changed, 7 insertions(+) > > diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h > index 3bac873..6afad49 100644 > --- a/linux-headers/linux/kvm.h > +++ b/linux-headers/linux/kvm.h > @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { > #define KVM_CAP_DISABLE_QUIRKS 116 > #define KVM_CAP_X86_SMM 117 > #define KVM_CAP_MULTI_ADDRESS_SPACE 118 > +#define KVM_CAP_PHY_ADDR_WIDTH 119 > > #ifdef KVM_CAP_IRQ_ROUTING > > diff --git a/target-i386/kvm.c b/target-i386/kvm.c > index 066d03d..66e3448 100644 > --- a/target-i386/kvm.c > +++ b/target-i386/kvm.c > @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > uint64_t shadow_mem; > int ret; > struct utsname utsname; > + int max_phys_bits; > > ret = kvm_get_supported_msrs(s); > if (ret < 0) { > @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > } > } > > + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); max_phys_bits seems generic enough and could be applied to other targets as well. making it a property of machine, would make accessing/manipulating it easier. define default value for machine/TCG mode and when KVM is enabled it would override/set its own limit. then any board could easily access machine->max_gpa to make board specific checks. > + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) > + fprintf(stderr, "Warning: The amount of memory assigned to the guest " > + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); > + > if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { > smram_machine_done.notify = register_smram_listener; > qemu_add_machine_init_done_notifier(&smram_machine_done); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 09/07/2015 10:26, Laszlo Ersek wrote: >> > >> > Perhaps KVM could simply hide memory above the limit (i.e. treat it as >> > MMIO), and the BIOS could remove RAM above the limit from the e820 >> > memory map? > I'd prefer to leave the guest firmware*s* out of this... :) > > E820 is a legacy BIOS concept. In OVMF we'd have to hack the memory > resource descriptor HOBs (which in turn control the DXE memory space > map, which in turn controls the UEFI memory map). Those HOBs are > currently based on what the CMOS reports about the RAM available under > and above 4GB. > > It's pretty complex already (will get more complex with SMM support), > and TBH, for working around such an obscure issue, I wouldn't like to > complicate it even further... > > After all, this is a host platform limitation. The solution should be to > either move to a more capable host, or do it in software (disable EPT). The reason I mentioned the firmware is because you could in principle have the same issue on real hardware - say putting 128 GB on your laptop. The firmware should cope with it. If OVMF does not use etc/e820, it can instead hack the values it reads from CMOS, bounding them according to the CPUID value. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Laszlo Ersek <lersek@redhat.com> writes: ... >>> >>> First, see my comments on the KVM patch. >>> >>> Second, ram_size is not the right thing to compare. What should be >>> checked is whether the highest guest-physical address that maps to RAM >>> can be represented in the address width of the host processor (and only >>> if EPT is enabled, but that sub-condition belongs to the KVM patch). >>> >>> Note that this is not the same as the check written in the patch. For >>> example, if you assume a 32-bit PCI hole with size 1 GB, then a total >>> guest RAM of size 63 GB will result in the highest guest-phys memory >>> address being 0xF_FFFF_FFFF, which just fits into 36 bits. >>> >>> Correspondingly, the above code would not print the warning for >>> >>> -m $((63 * 1024 + 1)) >>> >>> on my laptop (which has "address sizes : 36 bits physical, ..."), even >>> though such a guest would not boot for me (with EPT enabled). >>> >>> Please see >>> >>> http://thread.gmane.org/gmane.comp.bios.tianocore.devel/15418/focus=15447 >>> >>> So, "ram_size" in the controlling expression should be replaced with >>> "maximum_guest_ram_address" (which should be inclusive, and the <= relop >>> should be preserved). >> also with memory hotplug tuned on we should check if the end of >> hotplug memory area is less then limit, i.e.: >> >> pcms->hotplug_memory.base + hotplug_mem_size < 1ULL << max_phys_bits > > Seems reasonable, thanks for the hint! Thanks Igor and Laszlo, makes sense. I am wondering if this 1GB PCI hole is always fixed so that I can simply include that in calculating the maximum guest ram address ? Or do we have to figure that out every time ? > (The LHS in this instance is exclusive though, so equality should *not* > trigger the warning. "maximum_guest_ram_address" is inclusive, and > equality should trigger the warning. (Although equality seems quite > impossible in practice.)) > > Thanks! > Laszlo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Paolo Bonzini <pbonzini@redhat.com> writes: > On 09/07/2015 10:26, Laszlo Ersek wrote: >>> > >>> > Perhaps KVM could simply hide memory above the limit (i.e. treat it as >>> > MMIO), and the BIOS could remove RAM above the limit from the e820 >>> > memory map? >> I'd prefer to leave the guest firmware*s* out of this... :) >> >> E820 is a legacy BIOS concept. In OVMF we'd have to hack the memory >> resource descriptor HOBs (which in turn control the DXE memory space >> map, which in turn controls the UEFI memory map). Those HOBs are >> currently based on what the CMOS reports about the RAM available under >> and above 4GB. >> >> It's pretty complex already (will get more complex with SMM support), >> and TBH, for working around such an obscure issue, I wouldn't like to >> complicate it even further... >> >> After all, this is a host platform limitation. The solution should be to >> either move to a more capable host, or do it in software (disable EPT). > > The reason I mentioned the firmware is because you could in principle > have the same issue on real hardware - say putting 128 GB on your > laptop. The firmware should cope with it. Agreed, it's probably not a good idea to deviate too much from how real hardware would behave IMO. As a simplification of Paolo's idea, is it possible for qemu to completely ignore memory above the limit ? Will that break anything ? :) > If OVMF does not use etc/e820, it can instead hack the values it reads > from CMOS, bounding them according to the CPUID value. > > Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Igor Mammedov <imammedo@redhat.com> writes: > On Wed, 08 Jul 2015 18:42:01 -0400 > Bandan Das <bsd@redhat.com> wrote: > >> >> If a Linux guest is assigned more memory than is supported >> by the host processor, the guest is unable to boot. That >> is expected, however, there's no message indicating the user >> what went wrong. This change prints a message to stderr if >> KVM has the corresponding capability. >> >> Reported-by: Laszlo Ersek <lersek@redhat.com> >> Signed-off-by: Bandan Das <bsd@redhat.com> >> --- >> linux-headers/linux/kvm.h | 1 + >> target-i386/kvm.c | 6 ++++++ >> 2 files changed, 7 insertions(+) >> >> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h >> index 3bac873..6afad49 100644 >> --- a/linux-headers/linux/kvm.h >> +++ b/linux-headers/linux/kvm.h >> @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { >> #define KVM_CAP_DISABLE_QUIRKS 116 >> #define KVM_CAP_X86_SMM 117 >> #define KVM_CAP_MULTI_ADDRESS_SPACE 118 >> +#define KVM_CAP_PHY_ADDR_WIDTH 119 >> >> #ifdef KVM_CAP_IRQ_ROUTING >> >> diff --git a/target-i386/kvm.c b/target-i386/kvm.c >> index 066d03d..66e3448 100644 >> --- a/target-i386/kvm.c >> +++ b/target-i386/kvm.c >> @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> uint64_t shadow_mem; >> int ret; >> struct utsname utsname; >> + int max_phys_bits; >> >> ret = kvm_get_supported_msrs(s); >> if (ret < 0) { >> @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> } >> } >> >> + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); > max_phys_bits seems generic enough and could be applied to other targets > as well. I am a little clueless about other targets but is figuring this out from userspace as simple as it's on x86 (cpuid)? If not, then I agree, this could be made a generic value. Bandan > making it a property of machine, would make accessing/manipulating it easier. > define default value for machine/TCG mode and when KVM is enabled > it would override/set its own limit. > > then any board could easily access machine->max_gpa to make board specific > checks. > >> + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) >> + fprintf(stderr, "Warning: The amount of memory assigned to the guest " >> + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); >> + >> if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { >> smram_machine_done.notify = register_smram_listener; >> qemu_add_machine_init_done_notifier(&smram_machine_done); -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 07/09/15 21:11, Bandan Das wrote: > Laszlo Ersek <lersek@redhat.com> writes: > ... >>>> >>>> First, see my comments on the KVM patch. >>>> >>>> Second, ram_size is not the right thing to compare. What should be >>>> checked is whether the highest guest-physical address that maps to RAM >>>> can be represented in the address width of the host processor (and only >>>> if EPT is enabled, but that sub-condition belongs to the KVM patch). >>>> >>>> Note that this is not the same as the check written in the patch. For >>>> example, if you assume a 32-bit PCI hole with size 1 GB, then a total >>>> guest RAM of size 63 GB will result in the highest guest-phys memory >>>> address being 0xF_FFFF_FFFF, which just fits into 36 bits. >>>> >>>> Correspondingly, the above code would not print the warning for >>>> >>>> -m $((63 * 1024 + 1)) >>>> >>>> on my laptop (which has "address sizes : 36 bits physical, ..."), even >>>> though such a guest would not boot for me (with EPT enabled). >>>> >>>> Please see >>>> >>>> http://thread.gmane.org/gmane.comp.bios.tianocore.devel/15418/focus=15447 >>>> >>>> So, "ram_size" in the controlling expression should be replaced with >>>> "maximum_guest_ram_address" (which should be inclusive, and the <= relop >>>> should be preserved). >>> also with memory hotplug tuned on we should check if the end of >>> hotplug memory area is less then limit, i.e.: >>> >>> pcms->hotplug_memory.base + hotplug_mem_size < 1ULL << max_phys_bits >> >> Seems reasonable, thanks for the hint! > > Thanks Igor and Laszlo, makes sense. I am wondering if this 1GB PCI > hole is always fixed so that I can simply include that in calculating the maximum > guest ram address ? Or do we have to figure that out every time ? Please grep the tree for "above_4g_mem_size". The size of the 32-bit PCI hole is not constant, but all the necessary computation goes into "above_4g_mem_size" already. So I think you should derive the max possible gpa from "above_4g_mem_size" and the top of the hotpluggable memory area, and compare that against the PCPU address width, *if* EPT is enabled. (BTW "pcms->hotplug_memory.base" depends on "above_4g_mem_size" too.) Thanks Laszlo > >> (The LHS in this instance is exclusive though, so equality should *not* >> trigger the warning. "maximum_guest_ram_address" is inclusive, and >> equality should trigger the warning. (Although equality seems quite >> impossible in practice.)) >> >> Thanks! >> Laszlo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h index 3bac873..6afad49 100644 --- a/linux-headers/linux/kvm.h +++ b/linux-headers/linux/kvm.h @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info { #define KVM_CAP_DISABLE_QUIRKS 116 #define KVM_CAP_X86_SMM 117 #define KVM_CAP_MULTI_ADDRESS_SPACE 118 +#define KVM_CAP_PHY_ADDR_WIDTH 119 #ifdef KVM_CAP_IRQ_ROUTING diff --git a/target-i386/kvm.c b/target-i386/kvm.c index 066d03d..66e3448 100644 --- a/target-i386/kvm.c +++ b/target-i386/kvm.c @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) uint64_t shadow_mem; int ret; struct utsname utsname; + int max_phys_bits; ret = kvm_get_supported_msrs(s); if (ret < 0) { @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s) } } + max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH); + if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size) + fprintf(stderr, "Warning: The amount of memory assigned to the guest " + "is more than that supported by the host CPU(s). Guest may be unstable.\n"); + if (kvm_check_extension(s, KVM_CAP_X86_SMM)) { smram_machine_done.notify = register_smram_listener; qemu_add_machine_init_done_notifier(&smram_machine_done);
If a Linux guest is assigned more memory than is supported by the host processor, the guest is unable to boot. That is expected, however, there's no message indicating the user what went wrong. This change prints a message to stderr if KVM has the corresponding capability. Reported-by: Laszlo Ersek <lersek@redhat.com> Signed-off-by: Bandan Das <bsd@redhat.com> --- linux-headers/linux/kvm.h | 1 + target-i386/kvm.c | 6 ++++++ 2 files changed, 7 insertions(+)