On Tue, Sep 15, 2020 at 12:32:29PM +0200, Vitaly Kuznetsov wrote: > Wei Liu <wei.liu@xxxxxxxxxx> writes: > > > When Linux is running as the root partition, the hypercall page will > > have already been setup by Hyper-V. Copy the content over to the > > allocated page. > > And we can't setup a new hypercall page by writing something different > to HV_X64_MSR_HYPERCALL, right? > My understanding is that we can't, but Sunil can maybe correct me. > > > > The suspend, resume and cleanup paths remain untouched because they are > > not supported in this setup yet. > > > > Signed-off-by: Lillian Grassin-Drake <ligrassi@xxxxxxxxxxxxx> > > Signed-off-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx> > > Signed-off-by: Nuno Das Neves <nudasnev@xxxxxxxxxxxxx> > > Co-Developed-by: Lillian Grassin-Drake <ligrassi@xxxxxxxxxxxxx> > > Co-Developed-by: Sunil Muthuswamy <sunilmut@xxxxxxxxxxxxx> > > Co-Developed-by: Nuno Das Neves <nudasnev@xxxxxxxxxxxxx> > > Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx> > > --- > > arch/x86/hyperv/hv_init.c | 26 ++++++++++++++++++++++++-- > > 1 file changed, 24 insertions(+), 2 deletions(-) > > > > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c > > index 0eec1ed32023..26233aebc86c 100644 > > --- a/arch/x86/hyperv/hv_init.c > > +++ b/arch/x86/hyperv/hv_init.c > > @@ -25,6 +25,7 @@ > > #include <linux/cpuhotplug.h> > > #include <linux/syscore_ops.h> > > #include <clocksource/hyperv_timer.h> > > +#include <linux/highmem.h> > > > > /* Is Linux running as the root partition? */ > > bool hv_root_partition; > > @@ -448,8 +449,29 @@ void __init hyperv_init(void) > > > > rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > > hypercall_msr.enable = 1; > > - hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg); > > - wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > > + > > + if (hv_root_partition) { > > + struct page *pg; > > + void *src, *dst; > > + > > + /* > > + * Order is important here. We must enable the hypercall page > > + * so it is populated with code, then copy the code to an > > + * executable page. > > + */ > > + wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > > + > > + pg = vmalloc_to_page(hv_hypercall_pg); > > + dst = kmap(pg); > > + src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT, PAGE_SIZE, > > + MEMREMAP_WB); > > memremap() can fail... And we don't care here, if it fails, we would rather it panic or oops. I was relying on the fact that copying from / to a NULL pointer will cause the kernel to crash. But of course it wouldn't hurt to explicitly panic here. > > > + memcpy(dst, src, PAGE_SIZE); > > + memunmap(src); > > + kunmap(pg); > > + } else { > > + hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg); > > + wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64); > > + } > > Why can't we do wrmsrl() for both cases here? > Because the hypercall page has already been set up when Linux is the root. I could've tried writing to the MSR again, but because the behaviour here is not documented and subject to change so I didn't bother trying. Wei. > > > > /* > > * Ignore any errors in setting up stimer clockevents > > -- > Vitaly >