> -----Original Message----- > From: Jan Kiszka [mailto:jan.kiszka@xxxxxx] > Sent: Saturday, November 03, 2012 6:55 PM > To: Hao, Xudong > Cc: qemu-devel@xxxxxxxxxx; avi@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx > Subject: Re: [PATCH 1/2] qemu-kvm/cpuid: fix a emulation of guest physical > address space > > On 2012-11-02 06:38, Xudong Hao wrote: > > For 64 bit processor, emulate 40 bits physical address if the host physical > > address space >= 40bits, else guest physical is same as host. > > > > Signed-off-by: Xudong Hao <xudong.hao@xxxxxxxxx> > > --- > > target-i386/cpu.c | 5 ++++- > > 1 files changed, 4 insertions(+), 1 deletions(-) > > > > diff --git a/target-i386/cpu.c b/target-i386/cpu.c > > index 423e009..3a78881 100644 > > --- a/target-i386/cpu.c > > +++ b/target-i386/cpu.c > > @@ -1584,7 +1584,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t > index, uint32_t count, > > if (env->cpuid_ext2_features & CPUID_EXT2_LM) { > > /* 64 bit processor */ > > /* XXX: The physical address space is limited to 42 bits in exec.c. */ > > - *eax = 0x00003028; /* 48 bits virtual, 40 bits physical */ > > +/* XXX: 40 bits physical if host physical address space >= 40 bits */ > > + uint32_t a, b, c, d; > > + host_cpuid(0x80000008, 0, &a, &b, &c, &d); > > + *eax = a < 0x00003028 ? a : 0x00003028; > > This variation will not only affect -cpu host, right? That can create > problems when migrating between hosts with different address widths, and > then we will need some control knob to adjust what it reported to the guest. > Oh, I did not consider migrating to different platform(addr widths). But I think the fixed value 40 bits may cause problem: in VT-d case, when a host support GAW < 40 bits, and qemu emulate 40 bits guest physical address space, will bring bug on: drivers/iommu/intel-iommu.c static struct dma_pte *pfn_to_dma_pte(struct dmar_domain *domain, unsigned long pfn, int target_level) { int addr_width = agaw_to_width(domain->agaw) - VTD_PAGE_SHIFT; ... BUG_ON(!domain->pgd); BUG_ON(addr_width < BITS_PER_LONG && pfn >> addr_width); > Jan > > > } else { > > if (env->cpuid_features & CPUID_PSE36) > > *eax = 0x00000024; /* 36 bits physical */ > > > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
