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Drivers: hv: vmbus: Support >64 VPs for a fully enlightened TDX/SNP VM

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Don't set *this_cpu_ptr(hyperv_pcpu_input_arg) before the function
set_memory_decrypted() returns, otherwise we run into this ticky issue:

For a fully enlightened TDX/SNP VM, in hv_common_cpu_init(),
*this_cpu_ptr(hyperv_pcpu_input_arg) is an encrypted page before
the set_memory_decrypted() returns.

When such a VM has more than 64 VPs, if the hyperv_pcpu_input_arg is not
NULL, hv_common_cpu_init() -> set_memory_decrypted() -> ... ->
cpa_flush() -> on_each_cpu() -> ... -> hv_send_ipi_mask() -> ... ->
__send_ipi_mask_ex() tries to call hv_do_rep_hypercall() with the
hyperv_pcpu_input_arg as the hypercall input page, which must be a
decrypted page in such a VM, but the page is still encrypted at this
point, and a fatal fault is triggered.

Fix the issue by setting *this_cpu_ptr(hyperv_pcpu_input_arg) after
set_memory_decrypted(): if the hyperv_pcpu_input_arg is NULL,
__send_ipi_mask_ex() returns HV_STATUS_INVALID_PARAMETER immediately,
and hv_send_ipi_mask() falls back to orig_apic.send_IPI_mask(),
which can use x2apic_send_IPI_all(), which may be slightly slower than
the hypercall but still works correctly in such a VM.

Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230824080712.30327-6-decui@microsoft.com
This commit is contained in:
Dexuan Cui 2023-08-24 01:07:07 -07:00 committed by Wei Liu
parent 0719881bf8
commit cceb4e0810
1 changed files with 23 additions and 7 deletions
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30
drivers/hv/hv_common.c
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@ -360,6 +360,7 @@ int hv_common_cpu_init(unsigned int cpu)
u64 msr_vp_index; u64 msr_vp_index;
gfp_t flags; gfp_t flags;
int pgcount = hv_root_partition ? 2 : 1; int pgcount = hv_root_partition ? 2 : 1;
void *mem;
int ret; int ret;
/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */ /* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
@ -372,25 +373,40 @@ int hv_common_cpu_init(unsigned int cpu)
* allocated if this CPU was previously online and then taken offline * allocated if this CPU was previously online and then taken offline
*/ */
if (!*inputarg) { if (!*inputarg) {
*inputarg = kmalloc(pgcount * HV_HYP_PAGE_SIZE, flags); mem = kmalloc(pgcount * HV_HYP_PAGE_SIZE, flags);
if (!(*inputarg)) if (!mem)
return -ENOMEM; return -ENOMEM;
if (hv_root_partition) { if (hv_root_partition) {
outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg); outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
*outputarg = (char *)(*inputarg) + HV_HYP_PAGE_SIZE; *outputarg = (char *)mem + HV_HYP_PAGE_SIZE;
} }
if (hv_isolation_type_en_snp() || hv_isolation_type_tdx()) { if (hv_isolation_type_en_snp() || hv_isolation_type_tdx()) {
ret = set_memory_decrypted((unsigned long)*inputarg, pgcount); ret = set_memory_decrypted((unsigned long)mem, pgcount);
if (ret) { if (ret) {
/* It may be unsafe to free *inputarg */ /* It may be unsafe to free 'mem' */
*inputarg = NULL;
return ret; return ret;
} }
memset(*inputarg, 0x00, pgcount * PAGE_SIZE); memset(mem, 0x00, pgcount * HV_HYP_PAGE_SIZE);
} }
/*
* In a fully enlightened TDX/SNP VM with more than 64 VPs, if
* hyperv_pcpu_input_arg is not NULL, set_memory_decrypted() ->
* ... -> cpa_flush()-> ... -> __send_ipi_mask_ex() tries to
* use hyperv_pcpu_input_arg as the hypercall input page, which
* must be a decrypted page in such a VM, but the page is still
* encrypted before set_memory_decrypted() returns. Fix this by
* setting *inputarg after the above set_memory_decrypted(): if
* hyperv_pcpu_input_arg is NULL, __send_ipi_mask_ex() returns
* HV_STATUS_INVALID_PARAMETER immediately, and the function
* hv_send_ipi_mask() falls back to orig_apic.send_IPI_mask(),
* which may be slightly slower than the hypercall, but still
* works correctly in such a VM.
*/
*inputarg = mem;
} }
msr_vp_index = hv_get_register(HV_REGISTER_VP_INDEX); msr_vp_index = hv_get_register(HV_REGISTER_VP_INDEX);